It can output enough power for the GTX 770,but it's not a high quality PSU,so it may end up exploding and damaging the GPU.
I would recommend getting a Tier One,Tier Two Class A and Class B PSU found here: http://www.tomshardware.co.uk/answers/id-1804779/power-supply-unit-tier-list.html
Also,make sure that it's made by Rosewill,Seasonic,XFX,,EVGA or Cooler Master.
I can recommend you a Cooler Master V650,Rosewill Capstone 650W,XFX Core 650W and a Seasonic M12II 650W.