This part is a kind of semiconductor called AND8331.

Function of this product has Quasi-Resonant CurrentMode Controller.

Manufacturers : ON Semiconductor

Image and pinout :

Some of the text within the PDF file :

AND8331/D Quasi-Resonant CurrentMode Controller for HighPower ac-dc Adapters Prepared by: Stéphanie Conseil ON Semiconductor http://onsemi.com Introduction Pin Description This document describes the implementation of the DAP013 inside an AC-DC adapter. The DAP013 offers everything to build high performance AC-DC converters or offline adapters. Thanks to a novel valley lockout system, the controller is able to switch inside the drain-source valley and is immune to valley jumping instabilities. When the output load decreases significantly, the controller toggles to a fixed peak current/variable frequency mode that ensures very low standby power consumption. And last, but not least, the DAP013 features the usual protections that help to build cheap and safe power supplies: OVP, OTP, Brow [ ... ]

AND8331 PDF Datasheet Download