I want to use atx power from my pc as the source for my devices. How can i decide the footprint of the connectors, e.g. those with 20pins, 24pins, 4pins, ... Maybe i can goooogle them out using their formal names, but, what are they?
Also, keep in mind that PC power supplies generally have a minimum output current on one or more rails in order to stay in regulation. You generally won't be able to use them as a lab bench supply, unless you are careful to ballast up the outputs to their minimum output current when there is no other load. Just check the datasheet for the power supply you are considering, and look for the "minimum output load current" specification.
Concerning the minimum output current required, I once connected PS_ON# to ground as the connector was floating, and the fan did run. But I didn't test the output voltage, so I don't know if the power was working properly then. And it seems the manufacturers haven't provided detailed specification. What a pity if they can't be utilized in lab:(