Add Seasonic to the list of PSU makers that have clarified their support for Intel's upcoming Haswell processor. The next-gen CPU's low-power sleep states require only 0.05A on the 12V rail, down from 0.5A for Ivy Bridge. Supplying that little current on the 12V line causes problems for some PSUs, but most of Seasonic's units appear to be up to the task. Here's the word from the official statement:
Our full lines of 80 PLUSR Platinum and Gold power supplies have been designed to be ready to meet Haswell's new technical requirements! The ultra efficient Platinum series, which also includes the industry leading true fanless models, and our long running, award winning X Series, which is now supported by the 80 PLUSRGold G series - are all Haswell READY! In addition, our 80 PLUSRBronze line up, consisting of the M12II-650, 750 & 850W models, is also compatible to be used with Intel's new Haswell Processors.
Seasonic makes a handful of 80 Plus Bronze and Silver PSUs that aren't on the Haswell-ready list; most are inexpensive models with street prices under 65 bucks. It's unclear whether these units have been confirmed to cause problems with Haswell or if they simply haven't been validated for the platform.
According to Corsair, incompatible units can prevent Haswell systems from waking up from sleep properly. The PSU can "latch off," requiring manual power cycling using the switch at the back. Ugh.
Fortunately, we expect motherboard firmware to disable the offending C6/C7 sleep states by default. Manual intervention should only be necessary if you're sure you have a compatible PSU and want to enable the ultra-low-power modes.