A power supply circuit for charging a battery in a device to be charged, comprising: a primary rectifier unit, configured to perform rectification on input alternating current to output a first voltage having a periodically changing voltage value; a modulation unit, configured to modulate the first voltage to generate a second voltage; a transformer, configured to generate a third voltage based on the second voltage; a secondary rectifier and filtering unit, configured to perform rectification and filtering on the third voltage to generate an output current of the power supply circuit, the output current having a periodically changing current value; a current feedback unit, configured to receive the output current, and to send a feedback voltage to the modulation unit based on the output current, wherein the modulation unit is configured to perform modulating the first voltage to generate the second voltage based on the feedback voltage, to limit the current value of the output current to values below a preset current limit value: and a current sampling control unit, configured to receive the feedback voltage, to determine whether the current value of the output current is at a peak value based on the feedback voltage, and to sample the peak value of the output current when the current value of the output current is at the peak value, wherein the feedback voltage is a voltage at a feedback point coupling the input of the modulation unit to the output of the current feedback unit, wherein the current feedback unit is based on an operational amplifier; the power supply circuit further comprises: a pull-up unit, coupled between the current feedback unit and the modulation unit, and configured to pull up the feedback voltage to a high level when the operational amplifier in the current feedback unit is in a saturation state. a primary rectifier unit, configured to perform rectification on input alternating current to output a first voltage having a periodically changing voltage value; a modulation unit, configured to modulate the first voltage to generate a second voltage; a transformer, configured to generate a third voltage based on the second voltage; a secondary rectifier and filtering unit, configured to perform rectification and filtering on the third voltage to generate an output current of the power supply circuit, the output current having a periodically changing current value; a current feedback unit, configured to receive the output current, and to send a feedback voltage to the modulation unit based on the output current, wherein the modulation unit is configured to perform modulating the first voltage to generate the second voltage based on the feedback voltage, to limit the current value of the output current to values below a preset current limit value: and a current sampling control unit, configured to receive the feedback voltage, to determine whether the current value of the output current is at a peak value based on the feedback voltage, and to sample the peak value of the output current when the current value of the output current is at the peak value, wherein the feedback voltage is a voltage at a feedback point coupling the input of the modulation unit to the output of the current feedback unit, wherein the current feedback unit is based on an operational amplifier; the power supply circuit further comprises: a pull-up unit, coupled between the current feedback unit and the modulation unit, and configured to pull up the feedback voltage to a high level when the operational amplifier in the current feedback unit is in a saturation state.