The second link is a duplicate of the first so I'm not sure what your system specs are.
AMD recommends a 500w power supply for the 6850. It draws about 230w under load. Whether your 400w PSU is enough depends also on the amps on the 12v rail.
Further, low quality power supplies will often not be able to sustain the maximum wattage for long periods, so it depends on the quality of your PSU.
no, it pulls under 150W... mine pulls 140 and it's an "overclock" edition