An adapter, a portable electronic device and a charge control method thereof are provided. The adapter includes a connector and a controller. The connector includes a first terminal. The controller is electrically connected to the connector and determines whether to enter a quick charge mode according to a control signal from the connector. In the quick charge mod, the controller receives a charge control signal from the first terminal. The charge control signal has a plurality of pulses, and encoding information is formed by the plurality of pulses. The adapter is controlled by the controller according to the encoding information so as to provide a quick charge voltage.