Depends on the make and model of the PSU. A high quality unit will probably be ok with no OC or a lite OC. A low quality unit would probably puke on itself and die.
The 770 has a 230W TDP, at worst you'd see a rare 250W peak. So it should be fine on a quality 750W PSU, barring perhaps a highly overclocked FX-8350 or the like.
Depends on the make and model of the PSU. A high quality unit will probably be ok with no OC or a lite OC. A low quality unit would probably puke on itself and die.