Also, keep in mind that Empower is not exactly a 220 outlet -- sometimes if you run a laptop and charge it simultaneously, it will draw too much and shut down the adaptor. In that case, get the laptop running and then yank the battery -- it should run just fine.

If the little green light is not on the Empower port, ask a FA to ask the captain to turn the system on. (Generally find a younger one for this task; these kinds of requests really miff the grannies...)