The 8800 GTX & Ultra are made on 90nm. The GTX 280 uses a 65nm process.
The GTX280 uses around 30W more at full load than the 8800GTX, and if i remember, the Ultra used around 30W more than the standard 8800GTX, so, i guess that they need the same power +-. But, take care, cause, the new gfx cards are very sensible to the amperage in the 12V rails. You really need to balance the load between them, to feed your gfx card properly.