A power adapter, comprising: a full-bridge first rectifier circuit, configured to rectify an input alternating current and output a first voltage with a first pulsating waveform; a switch unit, configured to modulate the first voltage according to a control signal and output a modulated first voltage; a transformer, configured to output a second voltage with a second pulsating waveform according to the modulated first voltage, the full-bridge rectifier circuit being connected to a primary winding of the transformer without electrolytic capacitor; a second rectifier, configured to rectify the second voltage to output a third voltage with a third pulsating waveform; a first charging interface, coupled to the second rectifier, configured to apply the third voltage to a battery in a device via a second charging interface of the device when the first charging interface is coupled to the second charging interface, in which the second charging interface is coupled to the battery, wherein the second rectifier is connected to the first charging interface without electrolytic capacitor; a sampling unit, configured to sample current outputted by the second rectifier to obtain a current sampling value; and a control unit, coupled to the sampling unit and the switch unit respectively, and configured to output the control signal to the switch unit, and to control a charging process performed by the power adapter to a device to be in a constant current charging stage, which means that the peak value or mean value of the output current of the power adapter basically remains unchanged, by adjusting a duty ratio of the control signal when it is determined that current outputted by the power adapter is high or low according to the current sampling value. a full-bridge first rectifier circuit, configured to rectify an input alternating current and output a first voltage with a first pulsating waveform; a switch unit, configured to modulate the first voltage according to a control signal and output a modulated first voltage; a transformer, configured to output a second voltage with a second pulsating waveform according to the modulated first voltage, the full-bridge rectifier circuit being connected to a primary winding of the transformer without electrolytic capacitor; a second rectifier, configured to rectify the second voltage to output a third voltage with a third pulsating waveform; a first charging interface, coupled to the second rectifier, configured to apply the third voltage to a battery in a device via a second charging interface of the device when the first charging interface is coupled to the second charging interface, in which the second charging interface is coupled to the battery, wherein the second rectifier is connected to the first charging interface without electrolytic capacitor; a sampling unit, configured to sample current outputted by the second rectifier to obtain a current sampling value; and a control unit, coupled to the sampling unit and the switch unit respectively, and configured to output the control signal to the switch unit, and to control a charging process performed by the power adapter to a device to be in a constant current charging stage, which means that the peak value or mean value of the output current of the power adapter basically remains unchanged, by adjusting a duty ratio of the control signal when it is determined that current outputted by the power adapter is high or low according to the current sampling value.