
The power draw from the wall depends on the load.
I don't have any personal experience with dual PSes. Here are some numbers someone measured with a "kill-a-watt" meter -
http://www.hps.com/~...otebook/power.php
If the server needs 500 watts to run, it'll draw some fraction more than that from the wall (since the power supply isn't 100% efficient) - say 750 watts total.
I'd guess that you'll see very little additional power drawn from the wall with both supplies installed compared to a single supply. The server itself won't care as long as it gets the required voltages and currents, but the protection peripherals probably don't like running on just one power supply.
(Googlie-goo...)
Hmm. It seems that for at least some Dell servers, both power supplies are designed to supply half of the required power, and it switches to single-supply-mode if one fails.
http://serverfault.c...-ups-dell-servers That said, the power efficiency should still be only slightly worse than a comparable single power supply.
HTH a little.
Cheers,
Scott.