Within ONE year?!?
So Dell actually thinks customers will recoup between $180 and $400 in ONE YEAR of energy savings? How much do they think their customers are paying for electricity?!? Any decent modern power supply will use active power factor correction, so we can safely assume customers won't get hit with a power factor surcharge using either the Regular or Energy Smart servers. That just leaves the standard formula -- annual cost = kilowatt-hours x cost-per-kilowatt.
According to my provider in Massachusetts, WMECO, energy will cost "Small Commercial & Industrial" customers 11.467 cents (average) per kilowatt-hour from January through June 2008 (the variable monthly cost ranges from 10.424 to 12.719 cents per kWh). Assuming 24x365 operation (8,760 hours per year), at 11.467 cents per kWh, $270 is one year at 268.787 watts, $180 is one year at 179.191 watts, and $400 is one year at 398.204 watts. For some reason, I highly doubt that an Energy Smart server consumes 179.191, 268.787, or 398.204 fewer watts than a Regular server.