I have a PSU that I want to use to power two 120mm 12v fans. This power supply is not connected to a mother board. The fans came with an adapter to plug them into Molex cables. I have connected the power supply to the wall, and the fans to the molex cables coming out of it, however the fans will not run. The fan on the PSU does not come on either when i turn the PSU on, should it? I'm not sure if it is a faulty PSU or what.
The power supply may have a soft-on feature that requires the motherboard of a computer to switch it on. You can override that by jumpering the green wire to a black wire on the motherboard power connector. I'm not sure if that works for you since your power supply has a mechanical switch.
You may find that some of the info on this page regarding the power sense wire and other things to be useful.