A customer calls, saying her PC randomly switches off (sometimes 5 or 10 times per day).

I tell her it sounds like a faulty power supply, but she says that 4 months ago, a tech had replaced the motherboard and the power supply.

Well, I can’t resist a mystery, so I go take a look.

Sure enough, there is barely any dust on the MOBO and PSU fans, so its unlikely that its the PSU.

Murphy’s law says that while I’m there, the PC behaves itself, and I see no power outages.

We agree that I’ll replace the 350Watt PSU with a newer 450Watt unit.

If the problem persists, she will call me, and I’ll refund the cost of the PSU, and try to track down the problem.

Well, I haven’t heard back in over 4 weeks, so it looks like it was a faulty power supply (although unusual for such a new PSU to fail).