I am posting this item because I believe there is a total misunderstanding of the importance of having a healthy power supply in your computer.
From my recent experience in trying to get help to track down and fix the problem I was having with my computer see my Post “ Problems at mains switch on”. Had I followed the advice of so many computer experts including Dell I would have spent many hours reloading the operating system and other files and getting nowhere. The lesson I have learnt and think is worth passing on to anyone interested is simply this.
Just because the fan works and unplugging the power supply from the motherboard and checking all voltages are present and correct does not mean the power supply is not at fault!!!!!!!!!!!!!!!!.
Please let me explain. In my case the problem was resolved by replacing the ATX power supply. Out on the bench the power supply seemed to work perfectly OK starting up immediately on shorting the correct control pins. It was only when the standby voltage rail was given a resistive load that the voltage initially fell below that required to switch the computer on. On bench testing it is now taking 10mins at mains switch on for the standby voltage rail to reach the required +5v, which might suggest a fault in perhaps a soft start up timer circuit if it has one??????.
The power supply is now over 5 years old and several of the smoothing electrolytic capacitors were found on test to be in a very poor state. As a new power supply only cost £12 at a computer fair to replace I will not bother to repair it.
However examining the state of my power supply does suggest to me (I am no expert with computer software) that a lot of the problems with computer software malfunction especially when adding additional hardware or more powerful graphics cards could well be down to excessive ripple on the DC supplies to the motherboard made worse by the greater power demand due to failed electrolytic capacitors in the power supply especially if the PSU is several years old.
Does anyone have any thoughts on this?????

Electron Mick

Well, you still have some misconceptions yourself, but generally you are on the right track, with one MAJOR exception - your intent on buying a cheap £12 PSU. I like to put it this way; would you buy a nice new sports car then fill it up with generic, off-brand gas from Joe's Bait, Tobacco and Gas QuickieMart? You might, but would you expect it to run at peak performance? A gas engine can miss a beat and keep running - not so with digital electronics. Don't buy a cheap power supply.

I have written a lot on this subject as a quick search of this site will show. I have posted numerous times my canned texts on testing, sizing, and buying PSUs. I will include them below, but first, will address some of your points.

checking all voltages are present and correct does not mean the power supply is not at fault

That's right. But note that most users, even advanced users, do not have the capability to properly or conclusively test a PSU. That can ONLY be done under a proper load with an oscilloscope or power supply analyzer (not those plug in testers I mention below) in the hands of a "qualified" technician.

It was only when the standby voltage rail was given a resistive load that the voltage initially fell below that required to switch the computer on.

You got that backwards. The ATX Form Factor standard REQUIRES +5Vsb standby voltages to be present on several motherboard points when the PSU is simply plugged in (and IF equipped, the PSU master switch on back is set to enabled). The case's front panel power button does nothing more than "short" two pins on the motherboard's front panel header. A short removes resistance, not adds it. So when the PSU sees this short, it is signaled to turn on.

On bench testing it is now taking 10mins at mains switch on for the standby voltage rail to reach the required +5v, which might suggest a fault in perhaps a soft start up timer circuit if it has one??????.

No. There are no soft start timer circuits for computer power supplies. If it is taking longer than a few milliseconds for voltages to reach required levels, something is wrong - and if this is being tested on a bench without a realistic load, it is not a good test.

the state of my power supply does suggest to me (I am no expert with computer software) that a lot of the problems with computer software malfunction especially when adding additional hardware or more powerful graphics cards could well be down to excessive ripple

No. Software does not fail due to excessive ripple - hardware does. So if the HW fails, the SW stops. BUT - what does make troubleshooting problems much more difficult is a failing or weak PSU can manifest into all sorts of seemingly unrelated hardware and software issues, freezes, reboots, shutdowns, etc.

The problem with aging PSUs is not so much ripple, but simply age (helped along by heat) taking its toll on the components, and hardware upgrades. Power supplies get weaker over time. Users add more RAM and upgrade to more power hungry devices. Graphics cards are the most common as most folks just don't understand today's GPUs have 100s of millions MORE transistors on die than CPUs, and are much more power hungry.

That's not to say ripple is not a concern, it most definitely is - just not the only concern.

Here's my canned text on testing:

To properly and conclusively test a power supply unit (PSU), it must be tested under various realistic "loads" then analyzed for excessive ripple and other anomalies. This is done by a qualified technician using an oscilloscope or power analyzer - sophisticated (and expensive) electronic test equipment requiring special training to operate, and a basic knowledge of electronics theory to understand the results. Therefore, conclusively testing a power supply is done in properly equipped electronic repair facilities.

Fortunately, there are other options that are almost as good. I keep a FrozenCPU Ultimate PSU Tester in my tool bag when I am "in the field" and don't have a good spare power supply to swap in. While not a certain test, they are better than nothing. The advantage of this model is that it has an LCD readout of the voltage. With an actual voltage readout, you have a better chance of detecting a "failing" PSU, or one barely within specified ATX Form Factor Standard tolerances. Lesser models use LEDs to indicate the voltage is just within some "range". These are less informative, considerably cheaper, but still useful for detecting PSUs that have already "failed". Newegg has several testers to choose from. All these testers contain a "dummy load" to fool the PSU into thinking it is connected to a motherboard, and therefore allows the PSU to power on, if able, without being attached to a motherboard - great for testing fans, but again, it is not a true load or suitable for conclusive testing.

As mentioned, swapping in a known good supply is a tried and trued method of troubleshooting used for centuries, even by pros. Remove the "suspect" part and replace with a "known good" part and see if the problem goes away.

I do not recommend using a multimeter to test power supplies. To do it properly, that is, under a realistic load, the voltages on all the pins must be measured while the PSU is attached to the motherboard and the computer powered on. This requires poking (with some considerable force) two hard and sharp, highly conductive meter probes into the main power connector, deep in the heart of the computer. One tiny slip can destroy the motherboard, and everything plugged into it. It is not worth the risk considering most multimeters, like plug-in testers, do not measure, or reveal any unwanted and potentially disruptive AC components to the DC voltages.

And remember, anything that plugs into the wall can kill. Do not open the power supply's case unless you are a qualified electronics technician. There are NO user serviceable parts inside a power supply.

Here's my canned text on sizing and buying a new PSU:

Use the eXtreme PSU Calculator Lite to determine your power supply unit (PSU) requirements. Plug in all the hardware you think you might have in 2 or 3 years (extra drives, bigger or 2nd video card, more RAM, etc.). Be sure to read and heed the notes at the bottom of the page. I recommend setting Capacitor Aging to 30%, and if you participate in distributive computing projects (e.g. BOINC or Folding@Home), I recommend setting TDP to 100%. These steps ensure the supply has adequate head room for stress free operation and future demands. Research your video card and pay particular attention to the power supply requirements for your card listed on your video card maker's website. If not listed, check a comparable card (same graphics engine and RAM) from a different maker. The key specifications, in order of importance are:

1. Current (amperage or amps) on the +12V rail,
2. Efficiency,
3. Total wattage.

Then look for power supply brands listed under the "Good" column of PC Mechanic's PSU Reference List. Ensure the supplied amperage on the +12V rails of your chosen PSU meets the requirements of your video card. Don't try to save a few dollars by getting a cheap supply. Digital electronics, including CPUs, RAM, and today's advanced graphics cards, need clean, stable power. A good, well chosen supply will provide years of service and upgrade wiggle room. I strongly recommend you pick a supply with an efficiency rating equal to, or greater than 80%. Look for the 80 Plus - EnergyStar Compliant label. And don't forget to budget for a good UPS with AVR (automatic voltage regulation).

Hi
Thank you for taking the time and trouble to comment in such detail to my posting, which I have read with interest.
It was not my intention to buy “A Cheap” power supply, but a standard replacement. Sure, I could have paid much more for a PSU with three or four times the power rating and having a smart expensive fan to keep it cool, adding to the cost, together with eye catching packaging from the many brands available.
My local computer fair is in fact the largest computer fair in the South East of England held at the Ashburton School in Addiscombe South of London.
It certainly would not be in the interest of the regular traders at this fair held twice monthly to sell the sort of junk you may be referring too. “Joe’s Bait, Tobacco and Gas” would not stand a chance of getting a pitch at this place. Because of this it is a thriving venue for both the general public and trade buyers.

Looking at what is now on offer in the way of computer power supplies. Improvements in power supply chip design has resulted in higher switching speeds enabling smaller inductor and transformer core size to be used as well as smaller electrolytic capacitors to provide adequate smoothing and filtration, enabling the build cost to come down. However improvements in efficiency have not kept pace with the demand for more and more power, and this probably has lead to the present situation of many manufactures products failing to live up to their specifications. Even the best quote MTBF figures (>100,000 hrs), which I suspect are calculated from Ideal operating conditions for the components, not the true environmental conditions.
I am, therefore, under no illusions with the ATX500W power supply I purchased. All I can say is that on bench test prior to installation it performed well giving a clean set of regulated voltages up to the maximum load I was able to provide (I ran out of old plating bath load resistors at around 200W) but as I was only seeking to replace my Dell 250W unit I felt it should adequately meet my needs for the foreseeable future.

Only time will tell if the replacement power supply I have brought provides a useful life. It certainly proved a cheap way to confirmed my gut feeling that the problem at start up was in the power supply and not as suggested by many computer experts, a problem with the operating system
I will keep the original power supply, now refurbished, as a spare. The initial problem at mains switch on was due to drift within the TNY266P switching and control IC, which generates the +5v standby voltage, easy to replace.

In general I would not recommend anybody opening and attempting to repair a power supply. Certainly there would be no point in doing this from a service engineer’s point of view unless a suitable replacement was not available.

I was puzzled by your next comment, which suggests to me that you misunderstood what I was actually doing. I added a resistor to the standby supply line to the motherboard, not the start up control pin. Without a load on the standby supply line the full +5v was present on both the standby line and the start-up control pin from the word go, and on shorting this pin to ground the power supply started up immediately, with and without loads on the other voltage rails. However when I introduced a small load on the standby voltage rail before switching the mains on so as to simulate the permanent load placed on the standby supply by the motherboard’s voltage present LED’s and circuitry, both the motherboard standby voltage and the voltage across the start up control pin would then start at around 3.2v. With only this level of voltage across the control pin, shorting would not trigger start-up. However the voltage would rise very slowly over several minutes. At around 4.5v it was then possible to start up the power supply thereby reproducing the computer start up fault I had initially sort advice on.
Working without a service sheet it was of great help knowing there was no separate timer circuit to track down. Thank you.

You are of course quite right about software not failing. It is the running of the program within the microprocessor that concerns me.

Electron Mick

It was not my intention to buy “A Cheap” power supply, but a standard replacement. Sure, I could have paid much more for a PSU with three or four times the power rating and having a smart expensive fan to keep it cool, adding to the cost, together with eye catching packaging from the many brands available.

Whoa there Bud!!! I NEVER said anything about buying an oversized PSU in fancy packaging! I tend to choose my words carefully - please do not twist them about.

A replacement supply? That's much of the problem as many PSUs that come with PCs or cases are barely adequate to start with - with virtually no room for added RAM or a bigger graphics card. Therefore choosing a replacement is not a matter of buying a PSU with the same specs as before. Hence the need for a calculator and planning for future upgrades.

And for the record a £12 PSU is a cheap supply. And while a budget supply may do well to replace your ailing 250W supply, and while you feel it may support your needs for the foreseeable future, that is not the case for all. What if your motherboard fries in 6 months? Replacement boards for older systems are hard to find. This generally requires an upgraded board - which, in turn, requires a new CPU, RAM and maybe a graphics card too. Without buying for the future, you may have to buy yet another PSU to replace this one instead of being able to carry it over.

I think it important to say here for others reading that power supplies deliver what the computer needs, not what the supply is capable of. That is, if your computer needs 275W, the PSU will draw from the wall 275W (plus a little extra for efficiency loss and overhead) regardless if the PSU is a 350W supply or a 850W supply. So buying a bigger supply than you currently need does NOT result in higher electric bills. But, buying a better supply will likely result in lower bills as they tend to be more efficient.

Computer fairs? You seriously think junk supplies are not sold to bargain hunters at fairs? That's the perfect place to unload cheap supplies - including counterfeit supplies.

However improvements in efficiency have not kept pace with the demand for more and more power, and this probably has lead to the present situation of many manufactures products failing to live up to their specifications.

Again, you are sadly misinformed. Typical budget and older supplies were lucky to be 70% efficient. Today's better supplies are all 80% or better, with some approaching 90% - a remarkable achievement considering power supplies are inherently inefficient. And contrary to your statement, the bigger supplies (from good makers) tend to be more efficient than the lower wattage supplies as lower wattage supplies are closer to "entry level" models.

It certainly proved a cheap way to confirmed my gut feeling that the problem at start up was in the power supply and not as suggested by many computer experts, a problem with the operating system

Nothing wrong with that. I buy lots of cases that have cheap supplies tossed in, which I immediately pull and toss, but keep one or two on my bench for testing fans and drive motors. These are useful to swap in a computer for troubleshooting purposes.

In general I would not recommend anybody opening and attempting to repair a power supply.

Agreed. That's why I said there are NO "user serviceable" parts inside the PSU.

I was puzzled by your next comment, which suggests to me that you misunderstood what I was actually doing.

I did misunderstand - but my statement stands and as you determined, it should not take any significant time for the +5Vsb voltage to rise to a usable level.

Working without a service sheet it was of great help knowing there was no separate timer circuit to track down.

Sadly, manufactures don't make them available for those that know how to use them.

It is the running of the program within the microprocessor that concerns me.

No, it is the stability of the processor that matters - the actual data or program being crunched is immaterial.