Chip's power consumption is <6.6W/Ghs
ATX power loses(82%), DC/DC power loses(87%), Fan(5~20w), etc
So
650W * 0.82 * 0.87 - 20W =
443W, About right.
This is a business opportunity to make a high efficiency wall to dc converter.
Making a very focused product, well specified load and voltage, can allow the efficiency to be much higher.
There's a lot of server PSUs with a single 12V rail that are extremely efficient. You won't easily find a power supply that rectifies 120/240V AC down to 1.2V directly. It just becomes too difficult to have such a large difference between input and output voltage, and to deal with 500-1000A of current on the 1.2V rail.