http://www.anandtech.com/show/6953/s...ed-for-haswell

Good list from Anandtech.


Quote Originally Posted by Anandtech.com
The Haswell launch gets just a little more complicated each day, with the latest wrinkle being that standard ATX power supplies that conform to the ATX 2.3 standard may not actually be capable of supporting Haswell's extremely low power sleep states. The result has been power supply manufacturers scrambling to see if their power supplies can handle Haswell's requested 0.05A on the 12V rail as opposed to the ATX 2.3 minimum's 0.5A.
Emphasis added by me.

Basically, the new platform and CPU will enter a new extremely low power state if the PSU can handle it. (Apparently older PSU's can fail if the load on them drops below a certain threshold.)