A power supplying device is electrically connected to an alternating current (AC) power supplier and an electronic system. The power supplying device includes a rectifier, a power converter, a controller, a power manager, and a switch component. The power converter is electrically connected to the rectifier and includes a first electric power outputting terminal and a standby electric power outputting terminal. The standby electric power outputting terminal is electrically connected to the electronic system. The controller is electrically connected to the power converter. The power manager is electrically connected to the controller and the electronic system. The switch component is electrically connected to the first electric power outputting terminal, the power manager, and the electronic system. The switch component conducts or cuts-off an electric power outputted form the first electric power outputting terminal and transmitting to the electronic system according to controls of the power manager.