How can I diagnose a faulty power supply?

"Wow, interesting question.

The problem with diagnosing a power supply problem (when it's not hilariously obvious), is that the problem will often only show up under load, so even if you pull it out and check the voltage on every plug, you may not see any problems.

As many others have said, you can swap it with a ""Known Good"" power supply and see if the problem persists. You might also want to try to run some sort of benchmarking application to put the system under heavy load: if the system always crashes under load, regardless of the application, that's a good indicator of power supply problems."

Here's a great flowchart on diagnosing power supply problems. The guy's selling a book full of similar hardware troubleshooting flowcharts with solid discussion of what's going on. There are several available at the link for perusal. These are basic component-level troubleshooting charts, and don't get into tearing down the power supply to fix it, but these are all the basics in one reference:

Honestly, the easiest method might be to swap with a known good power supply. Failing that, you can also get power supply testers that will test various aspects of the power supply, such as verifying that all the voltage levels are within tolerances, etc.