I've run into two situations in the past two months where the power port at my seat was not working. In one case, it was then entire section where my seat happened to be (the first forward section in coach) and the other was just my seat alone. Obviously, there is no way of knowing whether the ports will be working at the seat that you select but don't be surprised if you are disappointed once on the plane.

If you find that the port light is not lit, the first thing that you should do is alert one of the FAs and ask them to turn the power to the power ports on. Apparently, this is a switch somewhere that has to be turned on for the ports to be "hot". In both of my failures, I did this first and it wasn't the source of the problem. Good luck.