Whenever I a wondering if a P/S is bad, I take a couple of old CDROM's or hard drives and plug them into it. I then completly disconnect it from everything else including the wall. On the main connector that was running to the motherboard, take a piece of wire and short pins 14 and 15 (green and the black next to it) and then plug the P/S in and turn on the switch if it has one on it. If it runs fine, chances are it is o.k., if not you have probably found your culprit. If you have a multimeter then you can also easily check voltages.
