Legally, no they don't have to give you anything. However, if the power outlet is a feature of your flight and it is advertised on their website as being available, you should push them. Tell them that you flew with them because of the outlet availability advertised on their website and if a lack of maintenance is the reason for it not being available for you, they should pay up. I'd be specific in the amount you want, and also reasonable. They may (and probably will) say no, but it doesn't hurt to try.