Yeah, but even my oldest machines, which are going on five years or more old, don’t have failing power supplies. I also support dozens of aging machines at work, and power supply failures remain uncommon yet vexing problems.

You are right, though, that my experience frames my problem solving approach. I don’t look at power supplies early in the process since I haven’t encountered a high percentage of situations where power supply failure was the root cause of a problem.

The worst part is that power supply failure can look like just about any other kind of problem. And it is arguably the hardest part to isolate: you can disconnect hard drives, memory, disk drives, video cards, network interfaces..and the computer should still work to some limited degree. Disconnecting the power supply without replacing it doesn’t tell you much at all 🙂

The “right” way to diagnose power supply failure is to use a multimeter, put the supply under load, and measure the output. But I think the last multimeter I owned was a $10 thing I bought when I was about 20 years old….it has been AWOL for a decade at least, and I’ve never really missed it.