I checked several technical reviews. The Nvidia GeForce 8800 GTS (512MB) isn't not a power hog. Luckily Tom's Hardware did a detailed article about how much power video cards need that included the 8800 GTS in SLI mode. The article included actual test results.
Below is a link to the actual power consumption charts. Please note all measurements are for total power draw at the wall outlet (mains). In other words it is total power consumption for the entire pc system. I think you'll find it interesting.http://www.tomshardware.com/reviews/geforce-radeon-power,2122-6.html
Power supply calculators and video card manufacturers estimates and recommendations are just that and nothing else. Both are overestimated. There is a very good reason for that. Manufacturers know people will buy cheap, low budget, low quality power supplies of questionable performance and quality.