Re: Replacement for an AMD K6-2 500?
 

I've seen one system smoke... the case speaker wire came off, and shorted the 5v

Not sure there's anything else you can do with an old/left PSU - if the electrolytics wanted to make a mess, they'd probably have done it by now - just make sure the fan is good, in fact, if that's going to be running unattended, I'd open up the PSU and swap a new fan in pre-emptively.

If it's an AT PSU, not even sure that you could source a new spare now, not at any sensible price