Haswell has a function which makes them consume almost no power and so called "0 Load" when Idle.
But not all PSU's support this. I don't know details but what I know is if you're running it on a incompatible psu, then instead of going to "0 load" state, the PSU will just shut off turning your computer off and will require you to turn it on again. All psu brands have released the list of their psu's which are compatible with the Haswell.
1. Seasonic
These are the PSU's seasonic announced to be compatible with Haswell:
- X Series
650 W
750 W
850 W
1050 W
1250 W
Platinum
660 W
760 W
860 W
1000 W
1200 W
Platinum Fanless
400 W
460 W
520 W
M12II
650 W
750 W
850 W
G Series
360 W
450 W
550 W
650 W
The following Seasonic psu's are not compatible with haswell:
M12II: 520 W, 620 W
S12II: All
M12D: All
SS: All
2. Corsair
Check > Corsair Website < for list with details.
3. OCZ
Check > OCZ Website < for list and details.
These 3 brands are the only one I looked into. Will update if I come across something new.