Yea, I’m not ruling out a string of bad luck just causing all of the really old hardware to fail at the same time. As for your idea of unstable electricity, both PCs were plugged into a surge protector (not simultaneously), and the laptop was plugged into a completely separate surge protector in a different room. Doesn’t seem likely, but at the same time I’m not particularly knowledgeable on that front
I guess I could be jumping to conclusions with the laptop, but I did a test with the PCs and I’m pretty sure it’s the PSU. Both PCs are identical because my friend and I used the same list of parts to build them over a decade ago. Mine died a little bit after installing Mint, and since my friend has a more recent build, he let me salvage his PC for parts. First thing I did was see what happens if I just put his PSU in my dead PC and it immediately booted back up. However, I was concerned that maybe some other bit of hardware in my PC caused the PSU to fail, so I just put my hard drive and the working PSU back into my friend’s PC and used it as normal. About a month after that, it died the same way.
As for the other things you’ve suggested, I did try all of those tests to no avail, as well as cleaning/dusting all of the internals and connection ports with compressed air. I got nothing, which is why I figured I’d ask here.
And yet look at his left hand (honk honk)