Three different YouTube reviewers I follow all did videos on those cheap testers last year, and every single one found the same thing. They basically only check if the rails are alive, not if they can actually hold voltage when the PSU is working hard. I remember one guy hooked up a power hungry GPU and watched the 12V line drop to 11.2 while the tester still showed green. It's like checking if a water pipe has water in it by looking at it, instead of turning on the tap. Your story is a good warning for anyone who thinks those little tools are a real diagnosis.

I remember being at a family reunion maybe five years back and watching my uncle put in foam earplugs just to get away from the noise of twenty people talking at once. He sat there smiling with a glass of tea, and that stuck with me. It hit me later that most folks don't use sound gear for fancy work stuff, they use it to find a little quiet in a world that never shuts up. So these muffs with mics, they're not just for shops. They're part of a bigger thing where we're all just trying to pick out the one sound we need without losing our hearing to everything else. If they let you hear that knock tone, that's your quiet, and I bet that young fella found his somewhere else entirely.