Intel's fourth-generation Core processors are nearly here, otherwise known as Haswell. These processors feature C6/C7 low-power states, and are able to shift gears into a much more power efficient form of sleep.
Well, it looks like most power supplies aren't compatible with this new method, as they aren't able to deliver less than 0.05 amps across the 12V2 rail. The news comes from VR-Zone and has been backed up by The Tech Report, with some words from Corsair's Robert Pearce. Older power supplies, or cheaper models, won't get anywhere near the required low-power that the Haswell processors require, meaning that some systems will experience stability problems, or worse.
The problem worsens, as most power supply makers don't state their PSUs 12V2 rail specifications, making it hard for users to find out whether their PSU is capable of the low-power state or not. Corsair's Robert Pearce has said that he expects most motherboard vendors to disable C6/C7 by default in the BIOS as there are too many PSUs on the market that don't support the C6/C7 low-power state. Pearce said that Corsair is working on making sure that all of their PSU units are C6/C7 compliant.