1.5 years ago I built PC with following specs:
Soltek SL67EV1 motherboard, Pentium III 450 MHz Katmai, 384 MB of RAM(3 sticks by 128 MB), AGP Radeon 9200(Originally it was GeForce MX440 but it failed with artifacts), 3com Etherlink XL network card, 5-usb 2.0 PCI card, S3 ViRGE DX and ISA SB16 clone(3D Melody, which turned out to not produce sound because I forgot about -5V rail but it's not main issue for now, I can just put more modern soundcard or install that Voltage Blaster thing).

Disc drives: 80 GB Hitachi Deskstar, Fujitsu 2 GB HDD, LG IDE DVD drive

So, I installed relatively modern 2011 500w off-brand PSU in it from my other PC(which sometimes failed to power with that PSU so it was technically already bad, but I thought that with more low-power system it would work fine). It did initially worked fine, but I got issues with disc drives.

Issues: Windows got randomly corrupted with protection error, Debian install too got corrupted with GRUB2 going into rescue mode, or boot record completely not being detected or blinking "-" symbol being stuck infinitely. Even DVD sometimes failed to boot and I had to reburn it(despite other PC showing that disc is fully compilant with checksum after burning it in ImgBurn)

I firstly blamed on bad IDE cable because somehow it said that I have 40-pin cable despite it being 80-pin. So I bought ASUS and ABIT-branded IDE cables instead of noname gray 80-pin. But it didn't changed much. Additionally I thought that it could be bad IDE controller, but was(and still) unsure about this.

So I put this build on hiatus, but later I found another issue: HDD or DVD failing to spin when I connect few of drives. It beging to spin and then stops and tries to do that again. caused for system to work fine. I too thought "ah, probably IDE controller is bad and can't do stable data transfer with multiple discs". Leaving only one HDD without any other drives connected caused system to work fine. I hadn't gave it much thougt and put it on second hiatus.

But recently when I returned again to this build I decided to check MOLEX connector with multimeter. One disc power wire(that had unfortunately only one MOLEX connector, but in which HDD worked fine without respinning loop) had 5 volts, while other disc power wire with one sata power and two MOLEX with connected DVD drive that failed to spin properly showed just 4.17 volts.

I feel so stupid for missing this very obvious culprit, as it caused this issue. So now I am thinking about replacing PSU with new one. But will modern PSU handle that hardware? Are disc errors, data corruptions just as PSU issue or can IDE controller actually be faulty? Were MX440 artifact failure just random problem from age(cooling fan on it was working by the way) or were they caused by PSU? Should I be paranoid for my passive cooled Radeon 9200 failing either from overheating because I don't trust small radiator?