Its likely your outlet was just going bad. Happens to me quite often, particularly on the older United 747's. Keep plugging it in and out, jiggle it, and it may work at exactly the right angle (watch the green light). Also, sometimes, it will go out but then will come back on after being plugged in for a while. Not ideal, I know.

If you catch it early during the boarding process on an international flight where you still have 15-20 minutes before the door closes, report it to the FA right away. I did that once and it only took them a few minutes to replace the outlet. I was sitting in Global First, so maybe they made more of an effort to fix the problem. I realize you say it was working then stopped.