i know that it's connect the green to the black on a ATx so it will run without being connected to a motherboad .. but i don't know what it is for a AT power supply ? anyone know?
AT has a four-wire (some have just two) lead group that go to the power switch. Closing the power switch connects brown to black and blue to white. An AT power switch is just a DPST switch, but it carries mains current, so it can zap you good. Use great caution when handling live connections on an AT supply.
I think with the AT (as with ATX) supplies it may be important to have some dummy loading. A 4R7 10W resistor on the 5v line should be enough.
Good point, I've seen behavior ranging from extremely poor regulation all the way to "doesn't appear to start" without load present.
every AT I charged up without a connection on the motherboard end worked fine, the atx needed a wire.