6 - 8% is high, less than 5% is more typical, with less than 1 for the big names that conduct better quality control. Still, until human can create materials with zero impurities and zero tolerances, failures will occur.

your right perhaps a bit high that was just a number I saw on an online article once, but my point is no company ever has 100% of their parts come out good.

but my point is no company ever has 100% of their parts come out good.

Very true. And since power supplies and motherboards are made up of many parts from many sources, all may be "within specifications" individually, but when all the slight variances of individual components are added together, or if there is slight variance in the assembly process, suddenly the end result of the circuit or main assembly is out-of-tolerance, and the product fails. A lot has to go right for any device to work properly - most companies do a pretty good job of it - or they just don't last.