Broken power jacks are a common problem. I can not tell you how many times I see a laptop being taken out of the carrying case with the AC adapter still plugged into the unit. A fair share of the time, if they did not have a problem with either the AC adapter or the input jack, they do now. Leaving it in like this puts way too much stress on these parts and they will break. Always disconnect the adaptor and wrap the cords neatly when traveling.
Tripping over the AC adapter cord is probably the next biggest reason for failure. We know better than to stretch the cord across a walking path but we do it anyway, then suffer the consequences when it gets tripped on and the laptop gets pulled to the floor, or the power connector gets ripped out. Definitely no winners here. Just expenses.