I'm working on a "virtualization machine" - a computer for hosting virtual computers - and I'm doing some research on the power supply in it. The case is an Antec NSK2400, and the power supply, as the title says, is an Antec SU-380.
What I've found is that it has between a 70 and 85% efficient rating, depending upon the amount of energy used. Its too bad that the low end gets such low efficiency - less than 70% for around 40 Watts.
Since my system doesn't need a lot of juice, I might end up switching the power supply.
I have a SeaSonic S12 330, and it gets about the same level of efficiency.