A power adapter, comprising: a full bridge rectifying circuit, configured to rectify an alternating current without an electrolytic capacitor to output voltage in a first pulsating waveform; a first switch circuit, configured to modulate the voltage in the first pulsating waveform according to a control signal; a transformer, configured to output voltage in a second pulsating waveform based on the modulated voltage in the first pulsating waveform; a second rectifying circuit, configured to rectify the voltage in the second pulsating waveform without an electrolytic capacitor to a voltage in a third pulsating waveform; a first charging interface, coupled to the second rectifying circuit and configured to apply the voltage in the third pulsating waveform to a battery of a device through a second charging interface of the device when the second charging interface of the device couples to the first charging interface, wherein the battery is coupled to the second charging interface; a first current sampling circuit comprising a first resistor and a second resistor, wherein the first resistor is smaller than the second resistor, and being configured to sample current outputted by the second rectifying circuit to obtain a current sampling value, the first current sampling circuit selectively operable in a first current sampling mode, in which the current is detected through the first resistor, and a second current sampling mode, in which the current is detected through the second resistor; a second switch circuit, configured to control the first current sampling circuit to switch between the first current sampling mode and the second current sampling mode; and a control circuit, coupled to the first current sampling circuit, the first switch circuit, and the second switch circuit, the control circuit configured to output the control signal to the first switch circuit, configured to control the second switch circuit to control the first current sampling circuit to operate in the first current sampling mode in a fast charging mode or to operate in the second current sampling mode in a standard charging mode, and configured to regulate a duty cycle of the control signal according to the current sampling value so that the voltage and the current in the third pulsating waveform satisfy, respectively, a required charging voltage and current. a full bridge rectifying circuit, configured to rectify an alternating current without an electrolytic capacitor to output voltage in a first pulsating waveform; a first switch circuit, configured to modulate the voltage in the first pulsating waveform according to a control signal; a transformer, configured to output voltage in a second pulsating waveform based on the modulated voltage in the first pulsating waveform; a second rectifying circuit, configured to rectify the voltage in the second pulsating waveform without an electrolytic capacitor to a voltage in a third pulsating waveform; a first charging interface, coupled to the second rectifying circuit and configured to apply the voltage in the third pulsating waveform to a battery of a device through a second charging interface of the device when the second charging interface of the device couples to the first charging interface, wherein the battery is coupled to the second charging interface; a first current sampling circuit comprising a first resistor and a second resistor, wherein the first resistor is smaller than the second resistor, and being configured to sample current outputted by the second rectifying circuit to obtain a current sampling value, the first current sampling circuit selectively operable in a first current sampling mode, in which the current is detected through the first resistor, and a second current sampling mode, in which the current is detected through the second resistor; a second switch circuit, configured to control the first current sampling circuit to switch between the first current sampling mode and the second current sampling mode; and a control circuit, coupled to the first current sampling circuit, the first switch circuit, and the second switch circuit, the control circuit configured to output the control signal to the first switch circuit, configured to control the second switch circuit to control the first current sampling circuit to operate in the first current sampling mode in a fast charging mode or to operate in the second current sampling mode in a standard charging mode, and configured to regulate a duty cycle of the control signal according to the current sampling value so that the voltage and the current in the third pulsating waveform satisfy, respectively, a required charging voltage and current.