A primary controller of a switching power supply and the switching power supply are provided. The primary controller includes an input voltage detection module which receives a detected signal and generates a detection signal; a controller module which receives a feedback signal and a current sampling signal of the switching power supply, and generates a control signal according to the feedback signal and the current sampling signal; a PWM signal generation module, receive the detection signal and the control signal, generate a PWM signal according to the control signal when the detection signal is the second level, and stop generating the PWM signal when the detection signal is the first level; and a power switch transistor, having a control terminal coupled with an output terminal of the PWM signal generation module.