I thought someone buying 770 sleeps on money. If so, then frying whole PC make little difference. He just goes and gets a new one.
To me, anything that have more than 400W, or quality 400W is enough for single card setup (single GPU). But I'm not an expert when it comes to PSU
If I would be sleeping on money, I would have bought myself a GeForce GTX TITAN, the fastest i7 CPU and 32GB RAM. But I haven't upgraded my Game PC in 2-3 years and I think it's time to upgrade my GPU since my CPU is still fine. Years ago I bought myself a GeForce 4 Ti4600 for about 540 euro, but after that card I have always bought mid-end GPU's (6600GT and 8600GT before my GTX460). This time I wanted to be a little more future-proof since I mostly play first person shooters like Crysis.