A power supply mode switching circuit and method switch between power supply modes of a power supply device dynamically based on an operating current required for operation of an electronic product, such that the power supply device supplies a supplying current corresponding to the operating current. The circuit comprises a sampling unit, an amplifying unit, a comparing unit. The circuit is disposed between the power supply device and the electronic product, samples the supplying current from the power supply device with the sampling unit, and converts the supplying current into a sampling voltage. The amplifying unit converts the sampling voltage into an amplifying voltage by voltage amplification and outputs the amplifying voltage to the comparing unit. After comparing the voltage level of a reference voltage and that of the amplifying voltage, the comparing unit generates a control signal for switching the power supple modes of the power supply device.