Abstract: A power adapter includes a primary side for receiving power from a mains power supply; a secondary side for providing operating and/or charging power, derived from the primary side, to an electronic device connected to the secondary side; presence logic for determining whether the electronic device is connected to the secondary side; and switching logic for turning off the primary side automatically when the presence logic determines the electronic device is not connected. The power adapter thus shuts itself down if no electronic device is attached, and automatically starts itself up when a device is connected to the power adapter and is thus needed. The power adapter may also include voltage detection logic that detects when the device is fully charged. The power adapter also shuts itself down when an attached electronic device becomes fully charged, and automatically starts itself up when the charged state of the electronic device falls below a predetermined level.