> The only thing I can guess is that it's the average efficiency of the power supplies? Googling suggests the most efficient server power power supplies availa

> The only thing I can guess is that it's the average efficiency of the power supplies? Googling suggests the most efficient server power power supplies available do indeed have average efficiencies of around 93% (e.g. http://goo.gl/R1HqV http://goo.gl/R1HqV ), so yup, that seems likely.