A power supply system includes data circuitry as well as power circuitry to generate DC power for use by a portable electronic device having a rechargeable battery. The DC power, ground and two signaling lines are provided in a power supply connector which detachably mates with an electronic device power input port. In response to a first signal from the electronic device transmitted over one of the signaling lines, the data circuitry provides an analog signal to the electronic device over the other signaling line. The electronic device determines a parameter level, such as a current level, of the analog signal, and based on the determined parameter level controls charging of its battery.