Incompatible power supply?

DFI Lanparty UT NF3 250gb motherboard
AMD Sempron 3100+ processor
Nvidia 7600GT GPU

Hi all,
I recently moved from the UK to USA, and as a result I had to replace my PC power supply as it was incompatible with 115 voltage.
My old PSU was an enermax noisetaker EG475AX-VE(G) 470w. I replaced it with a cooler master extreme power plus 460w. When I hooked it all up and hit the power button, the fans spun for a moment but then stopped, and the PC wouldn't boot up.
I assumed that either my motherboard/CPU had been damaged in the move somehow, or I'd been sold a damaged PSU, so to test it I took the power supply out of my wife's PC and tried it in mine, and it worked. I figured that meant the new PSU was at fault, but then just to be sure I put the new PSU into my wife's PC, and to my surprise that worked fine too!
So at the moment I can get both machines working, but it's not ideal because my wife's PSU is not powerful enough to run my PC with the graphics card installed. It looks like my PC is not damaged, and the PSU is not faulty either, they just don't work together. I was under the impression that all a PSU needed to do was provide sufficient power, I don't understand how it can be incompatible (all the connectors fit and everything). How would I go about testing what the problem is?

ps: I know it's a very out of date machine, please don't advise me to just throw it out and buy a new one: I wish I had the money for that!
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  1. Here are the specs of the PSUs:

    Old (enermax)

    AC INPUT: 230V, 50Hz, 3.5A

    DC OUTPUT: +3.3V 34A, +5V 40A, +12V1 16A, +12V2 15A, -12V 0.8A, +5VSb 2.5A, +3.3V & 5V 280W, Total power 470W

    New (cooler master)

    AC INPUT: 115/230V 60/60Hz 10/6A

    DC OUTPUT: +3.3V 22A, +5V 25A, +12V1 18A, +12V2 18A, -12V 05.A, +5VSb 2.5A (box doesn't say total power)

    I don't know the details for my wife's PSU, it's just the default one that came with her PC (dell dimension 3000). The graphics card in mine is AGP, it just has an ordinary 4pin connector for power which is plugged in.
    I tried pretty hard to get the rig working with the new PSU, I stripped the PC down to just motherboard and CPU and it still wouldn't power up, so I don't think it's anything to do with the new supply not being powerful enough (especially as the Dell one that's in there now is much smaller).
  2. I have tried using the enermax here, nothing at all happens when I turn it on.

    edit: found the specs for the dell PSU

    # +3.3V 20.0A
    # +5V 27.0A
    # +12VDC 17.0A
    # -12V 0.8A
    # -5V 0.3A
    # +5Vsb 2.0A

    seems to be less powerful except for the +5V rail and it works fine. Would the +5v really make all that much difference, even when I tested it with just the motherboard and CPU?
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