An alternating current (AC)/direct current (DC) adaptor is to be coupled electrically with an electronic device having an electrical property, and includes a DC/DC converter that receives a DC voltage signal and a control signal, and that adjusts the DC voltage signal according to the control signal to obtain an output DC voltage signal. A device discriminator receives the output DC voltage signal, and generates, according to the output DC voltage signal and the electrical property, a device indication signal set. A controller obtains a target value according to the device indication signal set, and outputs the control signal according to an initial value or the target value to control voltage value of the output DC voltage signal provided to the electronic device.