It's also important noting that you can't just draw all that current from one supply. If a supply says 600W, it usually means x W on the 12V CPU, y W on the 12V PCIe-additional cables, z W on the 5V/3.3V rails, etc. And in the end, x+y+z will end up adding to 600W.
A 600W supply can not provide 600W on its 3.3V line. If it could, it would come with chunky cables.