A power system applied to a handheld device including a battery, a first connecting port, a second connecting port, a first detector, a second detector, a power delivery controller, a control unit, and a switching element is provided. The first connecting port is electrically connected to the battery through a first charging path. The second connecting port is electrically connected to the battery through a second charging path. The first detector is electrically connected to the first connecting port to generate a first detection signal. The second detector is electrically connected to the second connecting port to generate a second detection signal. The control unit controls the switching element according to the first detection signal and the second detection signal to selectively electrically connect the power delivery controller to the first connecting port or the second connecting port and controls conduction statuses of the charging paths.