Except for 3 caps, all of the caps on a IIfx are Black-Tantalum Caps and are least likely to fail. 1 is the dreaded cap that leaks on all the Macs so it needs to be replaced, and 2 are large axial caps that should be replaced if you get them.

But you can always try to jump start the IIfx with a battery pack of 2 AA's. If the PSU is good, it will start up after a jump start. Here's a Youtube Video on how to do it.