I have been told that the outlets on the Airbus narrow-bodies only deliver 60-65W, max.
I can't speak to the accuracy of this, but I have since discovered that while my 85W Macbook charger is unusable on this aircraft - that is to say, when I plug the Macbook charger in, it acts as it would if the outlet were simply dead - my 45W Dell charger works just fine.
Take from this data point what you will.