Switch Mode Power Supply (SMPS), also known as switching power supply and switching converter, is a high-frequency power conversion device and a type of power supply. Its function is to convert a level of voltage into the voltage or current required by the user through different forms of architecture. The input of a switching power supply is mostly AC power (such as mains) or DC power, and the output is mostly equipment that requires DC power, such as a personal computer, and the switching power supply converts the voltage and current between the two.

Switching power supplies are different from linear power supplies. Most of the switching transistors used by switching power supplies switch between fully open mode (saturation area) and fully closed mode (cutoff area). Both modes have the characteristics of low dissipation. The conversion will have higher dissipation, but the time is very short, so it saves energy and generates less waste heat. Ideally, the switching power supply itself consumes no power. Voltage regulation is achieved by adjusting the turn-on and turn-off times of transistors. On the contrary, when a linear power supply generates an output voltage, the transistor works in the amplification area and consumes power itself. The high conversion efficiency of the switching power supply is one of its major advantages, and because the switching power supply has a high operating frequency, it can use a small-sized, lightweight transformer. Therefore, the switching power supply will be smaller and lighter than a linear power supply.

If the high efficiency, size and weight of the power supply are important considerations, switching power supplies are better than linear power supplies. However, the switching power supply is more complicated, and the internal transistors will switch frequently. If the switching current is not processed, noise and electromagnetic interference may be generated that affects other equipment. Moreover, if the switching power supply is not specially designed, its power factor may not be high.