I stopped assuming power supplies were fine without load testing | Computer Technicians - Freelance Forum - The Community for Independent Professionals
Yeah, the "if it turned on it was fine" idea is such a trap. I've been burned by that too. Like @tarar38 said, a good psu test doesn't mean the whole system is solid. I had a machine that would boot windows fine, but the second you opened a video file, instant reboot. Took forever to find it was the board. Now I just assume nothing is fine until I've really pushed it.
Ever wonder if a flaky motherboard is actually the problem instead of the power supply? I had a system that passed a psu load test but still crashed under heavy gaming. Turns out the motherboard's own power regulation was dying and couldn't handle the sudden demand from the cpu. Now I stress test the whole system together, because a good psu can't fix a bad board.