If Pin 7 has voltage (measured with a multimeter) but VCC (Pin 5) keeps cycling between 9V and 15V, the auxiliary winding or startup capacitor is faulty.
If you’ve landed on this article, you are likely holding a faulty or trying to integrate one into a custom project. Common in industrial displays, all-in-one computers, and medical cart monitors, the A20112 (often associated with brands like Delta, Lite-On, or Amigo) is a compact, high-efficiency switching power supply. Unfortunately, manufacturers rarely publish official schematics for OEM parts. a20112 power supply schematic
Without the exact turns ratio, repair is guesswork. Based on reverse-engineering an A20112-3A unit: If Pin 7 has voltage (measured with a