XSReviews has reviewed the Antec Earthwatts 500w and the Akasa Greenpower 500w

Unless you subscribe to the theory of a second ice age, you'll know that humans are slowly warming our planet up due to CO2 output. While computers -- probably -- play a small part in this global change, there is still an impact. Step in 80+ power supplies which promise above 80% efficiency throughout their output wattage range (20%, 50% and 100%). Today I have two such units, both rated @ 500w but from two different manufacturers.

Antec Earthwatts 500w and the Akasa Greenpower 500w Reviews