Catch-22. Without good capacitors, you cannot test the power supply.
All Macintosh computers from the original 1984 model to well into the 2000s are now suffering from capacitor failure. Recapping them is a requirement, not an option.
Powering up a power supply with bad capacitors can cause hideously expensive damage from leaked electrolyte creating shorts to places where none should be. I know, because I've had to repair such units from people that didn't know any better. It gets very expensive very quick.