This unit doesn't come with an external power supply.

This Williams Sound FM transmitter is a great device. To use it, first, connect it to your audio source. Remember, it doesn't have an external power supply, so you'll need to use your own compatible one. When using, keep it in a dry and cool place to avoid over - heating. For maintenance, clean it regularly with a soft cloth. Don't expose it to water or strong magnetic fields. If there are any issues, check the connections and the power supply first.