The invention relates to the testing field of a power supply, particularly to an auxiliary power supply circuit, comprising a switching power chip, a DC (direct current)-DC module, a first voltage stabilization module, a second voltage stabilization module, a positive and negative voltage conversion module and an isolated voltage stabilization module, wherein the input end of the first voltage stabilization module is connected with a 48V input power supply and the output end thereof is connected with the switching power chip; the output end of the switching power chip is connected with the control end of the DC (direct current)-DC module; the input end of the DC (direct current)-DC module is connected with the 48V input power supply and the other end thereof is a DC output end; the DC output end is connected with the feedback end of the switching power chip by the isolated voltage stabilization module; the DC output end is further connected with the input end of the positive and negative voltage conversion module and the input end of the second voltage stabilization module respectively; in combination with the switching power chip, input 48V is output by respectively converting into 5V, 3,3V and 5V via the DC-DC module.