An FM transmitter and power supply/charging assembly electrically coupleable with an MP3 player. The assembly includes a modular docking unit having a main body portion with a docking cavity therein, wherein the main body portion contains the FM transmitter and power/charging circuitry, with coupling means in the docking cavity for connecting the MP3 player with the FM transmitter and power/charging circuitry, to accommodate FM transmission by the FM transmitter of audio content when played by the MP3 player in the docking cavity of the modular docking unit, and adapted for transmitting electrical power through the modular docking unit and the power/charging circuitry therein, for charging of a battery of the MP3 player and/or powering of the MP3 player.