Well, I found this site to late, I put my spare ATX power supply in a Dell. Oops.. Does anyone know where to find schematics on power supplies and also, how to test the type that is turned on from the front panel, like a Dell is? Since it is wired through the mother board, the power supply doesn't supply ALL the voltages untill turned on.
Power supply units usually have a table on the side of them with the pin designations, voltages and current ratings. If there isn't one on your PSU, try here:
[censored] Sorry, guests aren't allowed to post hyperlinks!
Interestingly enough, I searched on google for "atx power supply pinout diagram" and it brought me right back to this site! It's a small world... :-)
Oh BTW, the colours in this table are the same for all the cables coming from the PSU and not just the ones connected to the motherboard. So the yellow cable going to your HDD or whatever is still +12V. However be aware that the cable colours used by your PSU may be different: for example the +3.3V cables in my PSU are coloured purple. You might like to make your own table for personal referance, so you don't make any mistakes.
In what way are you intending to 'test' the power supply? I assume to find the voltages of the pins, or to see if they are all working?
I've never really needed to turn on a 'soft' ATX power supply - one that turns on through the mobo instead of having a switch in the mains power cable. However, I assume that you just have to short the relevant pin to ground. My guess is that you'd have to short pin 9 to ground, though I'm not sure which ground!. You could check the pins with a voltmeter when the power supply is switched off; presumably when the power supply is switched off, all the pins will be dead except for the pin going to the power switch. Check which pins have a voltage between them, decide which seems like the best option - either the most relevant sounding one, or the least damaging-sounding one! Get some pliers or something, and short them!
"I take no responsibility for any damages, be they direct, inconsequential..." :D
I can't say I like the look of pin 8... It looks like the mobo has to provide some kind of feedback to say the power is ok... I dunno. I think you should be alright though. Might as well try!
connect pins 11 (ps on) to pin 12 GNd for the NON StD DELL
STD ATX would be pin 14 to pin 13 or 16
Hope this helps