ON Semiconductor’s app note featuring 12V 12W adaptor design using NCP1362 primary side regulation controller with valley lockout that hold its switching frequency at light loads. Link here (PDF)
Quasi−square wave resonant converters also known as Quasi−Resonant (QR) converters are widely used in the adaptor market. They help designing flyback Switched−Mode Power Supply (SMPS) with a reduced Electro−Magnetic Interference (EMI) signature and improved efficiency.