Generally, in the B and C terminals, if you can find a gate that doesn't have a flight departing from it for a while, you'll be able to find an outlet behind the seats. Look for other people with laptops or phones plugged in. A West and F can be a bit more hit or miss - in the case of the former, if you're there, you're likely to be there when it's busy, and F has small gate areas without a lot of outlets.