The utility model discloses an auxiliary power unit, include: a rectifier module for being directed at the commercial power of input carries out the rectification, be connected with rectifier module for turn into the direct current of rectifier module output the galvanic switching power supply module of presupposition voltage value, be connected with rectifier module for with the DC conversion of the rectifier module output invertion power supply module for the alternating current of presupposition voltage value, a control module that is used for control switch power supply module and invertion power supply module to move, be connected with control module for the operation of response operator is to the switching control module of control module input power switch control signal. Combine switching power supply module and invertion power supply module in same set of control system, realized having satisfied the selectable outputs of multiple specification power in an electrical power unit handcart -type vacuum switch and carried out the demand of attribute testing to the different specification powers in scene. Simplify vacuum switch attribute testing auxiliary electrical power source's circuit structure, alleviateed weight, made things convenient for field test.