I checked several references. The Nvidia 480GTX video card uses a lot of power. Most technical reviews recommend an 800 to 850 watt power supply for a system with two 480GTX cards operating in SLI mode.
If they are available in your country, then Corsair and Seasonic are two brands that have a reputation for high quality power supplies that consistently earn high marks in technical reviews. They are reliable, stable, and come with a 5 year warranty. Some of the newer models come with a 7 year warranty. The warranty might be different in your country.