I assume your pc is a Dell Dimension 4200?
If so, I've attached the technical specs for the 4200. It includes all the pin out details (position, voltage, amps) for the PSU.
The 4200 PSU doesn't have any secondary power connections so provided that the voltage/amp levels match the replacement PSU, I can't see a problem.
All you may have to worry about then is getting it to fit the case.
Personally, if I've got any doubts about a PSUs voltage outputs, I just use a multimeter to check each one.