An electronic system sharing power with doorbell includes two power contacts, an AC switch, a first AC/DC conversion circuit, a DC switch, an electronic device, and a doorbell-driving device. The first AC/DC conversion circuit receives an AC power via the power contacts and generates a DC power according to the AC power. In a normal state, the AC switch is off and the DC switch is on. Therefore, the electronic device is powered by the DC power. When the electronic device receives an enabling signal, the electronic device controls the AC switch to be on, to cause the voltage of the doorbell contacts to change from a low voltage to a high voltage. The doorbell-driving device detects the voltage of the doorbell contacts and supplies the power to a doorbell according to the detected voltage.