Lots of electronic hardware gets problems its psu and more specificly: with the electrolytic capacitors.

How do old capacitors usually affect the capacitance of that electrolytic capacitor?

What effect does a bad electrolytic capacitor have on the input of the PSU?

What effect will have if the bad capacitor is on the output?

Note: I have measured the voltage several times and it is usualy correct but the electronic equipment only starts after replacing the capacitors.