Are these ATX supplies?
What should be happening, is that the PSU is detecting a false overload condition.
The motherboard connector might have some pins with two wires connected to them: the thinner wire is a voltage regulating line. The +12 and +5 lines at least, should have them. You can try cutting those, but I don't think it's going to be any help.
You're trying to force them on with some kind of load, right?
|