If the same scenario occurs with both PSU's - than only means that psu isn't the problem obviousely. Both of them are overloaded when turned on, and then they shut down.
Anyway, i't probably motherboard , but you still can try to isolate (and maybe fix) the problem. Unplug everything from the motherboard, including memory,video, ide cables(not sure about cpu though). Also unplug all cdroms hdd's , fd from the power supply, and turn the power on. Of course you can't expect a successfull POST (you guessed it) , but if power supply works continuosly and doesn't shut down - than you can plug your hardware back one by one and test each time untill you find the faulty one.