A reverse power supply method, comprising: mixing, by a power supply adapter, an x Digital Subscriber Line, xDSL, signal and Direct Current, DC; and transmitting, by the power supply adapter, a mixed signal to xDSL central office equipment through a subscriber line, wherein mixing, by the power supply adapter, the xDSL signal and the DC comprises: converting, by an Alternating Current-Direct Current, AC-DC, conversion circuit of the power supply adapter, input AC into DC, and transferring the DC to a first xDSL separator of the power supply adapter, and mixing, by the first xDSL separator, the DC and an input xDSL signal; or converting, by an AC-DC conversion circuit of the power supply adapter, input AC into DC, and transferring the DC to a first filter circuit of the power supply adapter, and mixing, by the first filter circuit, the DC and an input xDSL signal, correspondingly, the method further comprises: after mixing, by the first xDSL separator, the DC and the input xDSL signal, detecting, by a Power Supply Equipment, PSE, control circuit of the power supply adapter, whether there exists a Powered device, PD, and determining whether to supply power to the PD according to a detection result; or after mixing, by the first filter circuit, the DC and the input xDSL signal, detecting, by a PSE control circuit of the power supply adapter, whether there exists a PD, and determining whether to supply power to the PD according to a detection result, characterized in that detecting, by the PSE control circuit of the power supply adapter, whether there exists a PD comprises: detecting whether characteristic resistance of a PD detection circuit in the xDSL central office equipment is within a set resistance range and whether capacitance is within a set capacitance range; and determining that there exists the PD when judgment conditions of the resistance and the capacitance are met, and determining that there exists no PD when the judgment conditions of the resistance and the capacitance are not met. mixing, by a power supply adapter, an x Digital Subscriber Line, xDSL, signal and Direct Current, DC; and transmitting, by the power supply adapter, a mixed signal to xDSL central office equipment through a subscriber line, wherein mixing, by the power supply adapter, the xDSL signal and the DC comprises: converting, by an Alternating Current-Direct Current, AC-DC, conversion circuit of the power supply adapter, input AC into DC, and transferring the DC to a first xDSL separator of the power supply adapter, and mixing, by the first xDSL separator, the DC and an input xDSL signal; or converting, by an AC-DC conversion circuit of the power supply adapter, input AC into DC, and transferring the DC to a first filter circuit of the power supply adapter, and mixing, by the first filter circuit, the DC and an input xDSL signal, correspondingly, the method further comprises: after mixing, by the first xDSL separator, the DC and the input xDSL signal, detecting, by a Power Supply Equipment, PSE, control circuit of the power supply adapter, whether there exists a Powered device, PD, and determining whether to supply power to the PD according to a detection result; or after mixing, by the first filter circuit, the DC and the input xDSL signal, detecting, by a PSE control circuit of the power supply adapter, whether there exists a PD, and determining whether to supply power to the PD according to a detection result, after mixing, by the first xDSL separator, the DC and the input xDSL signal, detecting, by a Power Supply Equipment, PSE, control circuit of the power supply adapter, whether there exists a Powered device, PD, and determining whether to supply power to the PD according to a detection result; or after mixing, by the first filter circuit, the DC and the input xDSL signal, detecting, by a PSE control circuit of the power supply adapter, whether there exists a PD, and determining whether to supply power to the PD according to a detection result, characterized in that detecting, by the PSE control circuit of the power supply adapter, whether there exists a PD comprises: detecting whether characteristic resistance of a PD detection circuit in the xDSL central office equipment is within a set resistance range and whether capacitance is within a set capacitance range; and determining that there exists the PD when judgment conditions of the resistance and the capacitance are met, and determining that there exists no PD when the judgment conditions of the resistance and the capacitance are not met.