Virtual-Hideout posted a review on the Seasonic S12 500w Power Supply

Now keep in mind this 80% hold true when the power supply is delivering a certain amount of wattage. Below that wattage, some power supplies are not so efficient. The Seasonic SS-500HT stays really close to its described rating, which is what we all hope for. If you are in the market for an efficient and quiet power supply, pick up the Seasonic S12 500w.

Seasonic S12 500w Power Supply Review