A couple of days ago my PC's 24-pin ATX power supply began to make a bad, electrical burning smell. I took it off and replaced it with another (working) 24-pin supply I had lying around. That worked okay at the time but today it refused to switch on. So I took that one off and shorted power on and ground, hoping to test the voltages. The fan turned for a split second and then stopped. The pins and connectors did the same kind of thing - a low voltage appeared but quickly went back to zero. Another computer with a 24-pin motherboard also failed to make it do any more.
Just out of interest, I have plugged it into a computer with a 20-pin board, and it works fine! That draws me to the 4 extra pins, almost as if the original motherboard has done something to that part of the supply. But the original power supply with that board does still work other than the smell - it hasn't been shutting itself down or acting odd in any other way. And surely if one computer can power it on then the other ones should be able to as well?
Has anybody ever come across something like this?