Currently on board DL721 JFK-SFO. Freaked out when the lady next to me in 3B tapped me on the shoulder and asked if I knew how to turn up the volume on the IFE - she couldn't hear anything. I looked down and she had plugged the headphones (the DL-provided ones with two jacks) into the power outlet

Surprisingly nothing seemed to blow up and I think they still worked for her after I moved them into the proper outlet... but it makes me wonder. I expect there's some sort of fuse/breaker in the outlet, but I am amazed that the headphones didn't explode when she plugged them in.