Are there MP3 players that can play while plugged into power?

Q: I need some help on selecting an mp3 player. here is the application. I am loading the mp3 player with one 3 minute track which I need to play indefinitely on a loop. The headphone out gets plugged into a telephone on hold system. The track will loop over and over. So I need a player that can do continuous play. I also need a player that can play while connected to a power supply. (I am learning that not all players work when plugged into all). I definitely want I ow it has to be flash based so no moving parts. How long can an mp3 player play if no one ever touches it?