The most prevalent and infuriating problems with these computers are the power supplies and the lasers for the CD rom drive.

Generation 1 Tower card capacitor list. C6 must be a snap-in large capacitor. Everything else is regular/average spacing

Generation 2, 3 and 4 power supply cards are just as bad due to the cards being vertical and acid leaking sideways. C6 is a snap in super capacitor.
C12 will make a whining noise when the computer is off with the power standby mode near the relay K1. This is how you know it's about to die. C57 will also leak extremely badly.