Ok, here is what you want to do.
1. Plug in the PSU
2. Unattach the motherboard connectors
3. Take a paper clip and stick one end in the green wire on the 24-pin connector, and the other end into a black wire.
4. Measure the voltages with a multimeter, with the one probe in colored wire, and the other in any black wire.
This is what you should get:
Yellow--12v
Orange--3.3v
Red-5v
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