6770 to 7850

Hi guys! I just have a quick question. Currently I have a 6770 which runs perfectly fine in my system. I was wondering if I were to upgrade my GPU to a 7850, would the PSU requirements be the same? My PSU is a bit weak. It's a 400W low end PSU(Came in with the computer). However, based from the few sites I've seen, the 7850 seems to pull out just as much power as the 6770!

Thanks for the help in advance! Cheers!