Switching power supply and switching controller thereof

The invention discloses a switching power supply and a switching controller thereof. The switching power supply comprises a power converter, a current monitor, a switching controller, and a compensation resistor coupled between the current monitor and the switching controller. Through the compensation resistor and compensation current flowing through the compensation resistor, the voltage value of the current monitoring signal is inversely proportional to the input voltage. When the input voltage increases, the voltage value of the current monitoring signal decreases accordingly; and when the input voltage decreases, the voltage value of the current monitoring signal increases accordingly. The current monitoring signal indicates the current flowing through the primary winding of a transformer in the power converter. According to the switching power supply and the switching controller of the invention, the influence of the change in input voltage on the input power and output power of the power converter is reduced by use of the compensation current and the compensation resistor, so special application requirements of customers are satisfied.