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. <EOS>