why would you want to? you could but you would have to manually complete the power switch circuit by using a piece of wire to turn the psu on. i would not recommend you doing this
you could with the old at powersupplies. power button included. We used to hook up cd roms and put speakers to the earphone jacks and have a cheap cd player. But yes as EK said you would need something to jump it from. If you plug it into a mobo you can jump it from the pins where the power switch goes. Im also curious as to what your plans are for it.
yes its possible, no i wouldnt do it, youre going to fry something (most likely yourself) or blow something up, lol
something you can try tho, is if you have a voltage tester, plug in the PSU and put the testers in the red and black wire ports on the 4-pin power connectors