A power supply system for a magnetic bearing, comprising: a rectifying and filtering circuit, a power obtaining circuit, and a DC-DC power supply, wherein: the rectifying and filtering circuit is configured to rectify and filter an alternating current from an AC input power supply to obtain a first direct current with a first DC bus voltage, wherein the first direct current is configured to supply power to an electric motor controller of an electric motor to which the magnetic bearing belongs; the power obtaining circuit is configured to obtain a second direct current with a second DC bus voltage from the first direct current, wherein the second DC bus voltage is within an input voltage range allowed by the DC-DC power supply; and the DC-DC power supply is configured to convert the second direct current to a third direct current with a third DC bus voltage, wherein the third direct current is configured to supply power to a bearing controller of the magnetic bearing, the power supply system being characterised in that the power obtaining circuit comprises a control switch and a voltage dividing resistor which are arranged in parallel, wherein the control switch is configured to be: in an on state, in a case where the AC input power supply is not off and the first DC bus voltage is within a predetermined voltage range, to obtain the second direct current from the first direct current through a branch having the control switch; or in an off state, in a case where the AC input power supply is not off and the first DC bus voltage is higher than an upper limit of the predetermined voltage range, to obtain the second direct current from the first direct current through a branch having the voltage dividing resistor; or in an on state, in a case where the AC input power supply is off, to obtain the second direct current from power generated by the electric motor through the branch having the control switch. the rectifying and filtering circuit is configured to rectify and filter an alternating current from an AC input power supply to obtain a first direct current with a first DC bus voltage, wherein the first direct current is configured to supply power to an electric motor controller of an electric motor to which the magnetic bearing belongs; the power obtaining circuit is configured to obtain a second direct current with a second DC bus voltage from the first direct current, wherein the second DC bus voltage is within an input voltage range allowed by the DC-DC power supply; and the DC-DC power supply is configured to convert the second direct current to a third direct current with a third DC bus voltage, wherein the third direct current is configured to supply power to a bearing controller of the magnetic bearing, the power supply system being characterised in that the power obtaining circuit comprises a control switch and a voltage dividing resistor which are arranged in parallel, wherein the control switch is configured to be: in an on state, in a case where the AC input power supply is not off and the first DC bus voltage is within a predetermined voltage range, to obtain the second direct current from the first direct current through a branch having the control switch; or in an off state, in a case where the AC input power supply is not off and the first DC bus voltage is higher than an upper limit of the predetermined voltage range, to obtain the second direct current from the first direct current through a branch having the voltage dividing resistor; or in an on state, in a case where the AC input power supply is off, to obtain the second direct current from power generated by the electric motor through the branch having the control switch. in an on state, in a case where the AC input power supply is not off and the first DC bus voltage is within a predetermined voltage range, to obtain the second direct current from the first direct current through a branch having the control switch; or in an off state, in a case where the AC input power supply is not off and the first DC bus voltage is higher than an upper limit of the predetermined voltage range, to obtain the second direct current from the first direct current through a branch having the voltage dividing resistor; or in an on state, in a case where the AC input power supply is off, to obtain the second direct current from power generated by the electric motor through the branch having the control switch.