For some odd reason, NVIDIA gives the power requirements for their video cards in watts. Watts aren’t a very good quantitative measurement for this–there are both “good” and “bad” power supplies that have the same wattage rating, however they usually measure differently.
An article over at Spode’s Abode measures the power requirements of the 6800 Ultra. His consensus is that a 6800 Ultra requires a current of 5 amps at load, and can use a max of 124 watts power.
My 6800 GT is probably not far off. Along with the consideration that a modern high-end CPU will need 8 amps, and hard disks require ~2 amps each, I can plan my power requirements for a new system I’m building. More on that later.