Even a good 550 watt will do you good and yes i have the same problem it depends where your living, i have a corsair vs550, a cheap version from corsair and that happens. Reason: Because there might or might not be good power output from your house to your computer for eg. When the electricity switches off and it goes to battery power the PC could switch off as well or coming from battery power to electricity, same deal.
There is a little something in your PSU called Anti Surge search your BIOS under PSU options and turn that on if that has been turned off or check if you even have that option, mine doesn't
However if you find the Anti Surge option in your BIOS it still may or may not make a difference depending on the quality of the PSU and other components itself or even the stability of power output inside your house.
If neither of all these solutions work try getting a UPS battery for your PC, basically works as a stabilizer the same as a fridge. Once you upgrade to the GTX 770 make sure to get a minimum Bronze certified 600 watt PSU from either: Antec, XFX, Seasonic, Corsair and get back to us on tommers.