A power adapter, a cable, and a charger, where the power adapter includes an output port, a comparator circuit, and a voltage control and shaping circuit. The output port includes a voltage output terminal, a signal feedback terminal, a first ground terminal, and a second ground terminal. The comparator circuit is electrically connected to the signal feedback terminal, and is configured to compare a reference voltage with a charging input voltage of a to-be-charged device that is fed back by the signal feedback terminal to obtain a comparison voltage and output the comparison voltage to the voltage control and shaping circuit.