Chip's power consumption is <6.6W/Ghs
ATX power loses(82%), DC/DC power loses(87%), Fan(5~20w), etc
So
Yes, but those losses and loads were part of your power budget for 400 watts, correct? Don't be like Josh-- you were expecting less than 6.6 W/GH/s. Simulating the power performance of a chip like this is a lot more difficult problem than calculating how many watts you will need for the fans. Its completely understandable the simulations were slightly off, but still on the same order.