Not even close Kiiro. 7850 only has one PCIe connector, so its max is 150W. I believe its normally around 130W, same as the 6850. The GTX460 has two plugs, so its max is 225W, but uses around 170W depending on model/clocks. If he has the GTX460 now, the 7850 will run just fine.
Ah goodness, I feel quite stupid right now. Third edit.
I was reading the full system load consumption, not the card consumption. My mistake.