A GeForce 8800 GTX (Tesla G80 90nm GPU) draws about 28 Watts more than a GeForce 9800 GTX (Tesla G92 65nm GPU) during gaming.
A reference clocked GeForce 8800 GTX can draw 151 Watts during gaming and 176 Watts when running Furmark stability testing. That is just the graphics card only. The remaining components in your system will also need power from the +12V rail. The extra amount will depend on your system configuration.
There's no such card as a 9600GTS.