Many appliances and devices require auxiliary power supply (SMPS), which works separately from the main power supply to support (for example) standby operation. The rated power of these auxiliary power supplies varies from a few watts to several tens of watts, and they usually adopt an isolated or non-isolated structure. To ensure good performance, engineers must choose a power topology that best meets efficiency, size, safety, and cost requirements—including flyback or quasi-resonance.

In the 20-75W power range, the increasing efficiency and standby requirements of auxiliary power supplies have prompted designers to use quasi-resonant topologies to replace more mainstream flyback-based designs.