The invention discloses a switching power supply capable of achieving balanced adjustment of a bus. The switching power supply comprises a rectification circuit, wherein a bus output of the rectification circuit is connected with an input of a main loop of the switching power supply, the main loop of the switching power supply is connected with a pulse width modulation (PWM) control and sampling circuit and is used for providing a working voltage for the PWM control and sampling circuit, a PWM control signal generated by the PWM control and sampling circuit is connected with a power metal-oxide-semiconductor field effect transistor (MOSFET) control circuit, an output voltage generated by the main loop of the switching power supply is used for simultaneously providing a feedback voltage for the power MOSFET control circuit, and the power MOSFET control circuit controls on/off of a power MOSFET so as to control on/off of a primary winding of a power transformer of the main loop of the switching power supply. On one hand, the voltage required for each control circuit at the post stage can be met; and on the other hand, the voltage output from the rectification circuit at the front stage can be balanced.