A smart doorbell system, comprising: a chime circuit, comprising: a power connection terminal, configured to receive an alternating current, wherein the alternating current comprises a first direction current and a second direction current; a first rectifier circuit (140, 210), coupled to the power connection terminal; and a second rectifier circuit (150, 220), coupled to the power connection terminal and connected to the first rectifier circuit (140, 210) in parallel; a doorbell switch, coupled to the chime circuit in parallel; an input device, coupled to the first rectifier circuit (140, 210) and the second rectifier circuit (150, 220) and configured to generate a control signal, wherein the control signal respectively controls one of the first rectifier circuit (140, 210) and the second rectifier circuit (150, 220) to be activated for corresponding one of the first direction current and the second direction current from the power connection terminal of the chime circuit to pass through when the doorbell switch is turned off; and a ring circuit, coupled to the doorbell switch, wherein the ring circuit receives one of the first direction current and the second direction current to maintain power and produces a ringing sound according to a trigger signal, wherein the trigger signal is generated according to another one of the first direction current and the second direction current when the doorbell switch is turned on. a chime circuit, comprising: a power connection terminal, configured to receive an alternating current, wherein the alternating current comprises a first direction current and a second direction current; a first rectifier circuit (140, 210), coupled to the power connection terminal; and a second rectifier circuit (150, 220), coupled to the power connection terminal and connected to the first rectifier circuit (140, 210) in parallel; a power connection terminal, configured to receive an alternating current, wherein the alternating current comprises a first direction current and a second direction current; a first rectifier circuit (140, 210), coupled to the power connection terminal; and a second rectifier circuit (150, 220), coupled to the power connection terminal and connected to the first rectifier circuit (140, 210) in parallel; a doorbell switch, coupled to the chime circuit in parallel; an input device, coupled to the first rectifier circuit (140, 210) and the second rectifier circuit (150, 220) and configured to generate a control signal, wherein the control signal respectively controls one of the first rectifier circuit (140, 210) and the second rectifier circuit (150, 220) to be activated for corresponding one of the first direction current and the second direction current from the power connection terminal of the chime circuit to pass through when the doorbell switch is turned off; and a ring circuit, coupled to the doorbell switch, wherein the ring circuit receives one of the first direction current and the second direction current to maintain power and produces a ringing sound according to a trigger signal, wherein the trigger signal is generated according to another one of the first direction current and the second direction current when the doorbell switch is turned on.