720 watts should certainly be enough for the GTX275.
The psu is another unit that is hard to find info on, even Gigabytes own site doesn't provide much.
The specs say a single 6+2 pin pcie connector, the manual shows a 6 and a 6+2.
I have GTX275 1.7G and working fine with 700W. The sales said minimum is 550 and above 600 is fine. I got 700 got SLI in future use. But this Card requires 4 power connectors, which I had to buy extra one.
Intel i7 2.8G
Corsair 4G RAM 16000
320GB SATA HDD
basic intel P55 Motherboard
700W Power Supply
LG DVD RW
nVidia GTX 275 1792MB
Sound Blaster XiF Gamer
I ran my GTX-275 on the 530w Rosewill that is the first link I provided in the prior post until last week. No problems. I've also run a GTX-260 on it and a HD4850 w/o issues on any of the 3 cards. The quoted minimum wattages assume you're gonna go out and buy a 'Caca 585w' PSU for $24.99.
The only reason I am not still using it is I fell into a deal on a PC Power & Cooling Quad 750 for $20 new in the box and I need the 530w Rosewill for another 'puter that will probably have a GTX-275 card in it also.
Guess I'll have to get a new mobo and a pair of GTX-295s so I can justify this heavy overkill PSU now