I doubt it was the power supplu - you still have the problem! 
First of all, I can understand your concern. I hacve worked with eleftronic devices for several years and it is never easy to diagnoste a problem unless there is
a smoking gun. That is, some real specific prooof taht a componet or modual has vailes. Here are some rare thigns often overlooked:
A. Bad CD/DVD drive taht draws too much current.
(Tech has to use an amp probve to verify thjis.)
B. Hard drive with faiing motopr taht does not maintain speed
(Hard to verify.)
C. Memory stick that is sensitive to some paterns.
(Requires extensive testing.)
D. CPU that has an esoteric internal eror.
(Ccan not be vrified direcdtly with shope tools. A tech can try another CPU of the same part number. Belive me, there are a few bad CPUs out there. )
Item C above can be , to some exctent, verified with time and testing. You have to try just one stick in the machine, if posible, and run one of the tough multi-pass memory tests.
Here is one form Microsft. Once running, it does not depend of the OS. It tests the memory will paterens tht may revel some kind of internal flaw in the memory chips. You can do this test without anoth specail equipment.
https://technet.microsoft.com/en-us/library/2008.09.utilityspotlight.aspxOne of the PCs you support is acting up—freezing, crashing, blue screening. Is some piece of hardware failing? Is some newly installed application causing trouble? Or could it be faulty memory? One way to find out for sure is with the free Microsoft® Windows® Memory Diagnostic utility. This tool will run a variety of tests on your PC's RAM to determine whether flaws exist in any of the modules.
It is worht the effort. Might save your some time and money.
