Charger problems

I have an Alienware M14x R2, it's 4 months old. Sometimes when I plug the charger in the battery doesn't charge, I get "plugged in, not charging" showing on the battery icon. It has happened maybe 4 times, and either started working when I plugged the charger out of the wall and back in, or just by itself after a few minutes. Has any other Alienware users had this problem? I've seen a few threads with the issue, is it my charger or battery that's broke? Or is it something else?