A high-precision PC power adopter based on PFM control chip OB2269 has been designed. The power adapter adopts the fly-back topology structure, with PFM control its frequency modulation control mode, with the transistor active block circuit its auxiliary supply, with the isolated single output its output circuit, and with the composite structure of PC817 and TL431its voltage feedback circuit. The test results show that the PC power adapter of this design can output the high-precision 19.3 V, with its the power up to 100 W, with its efficiency as high as 78.8%, and with its ripple voltage 100 mV. The PC power adapter, low in production cost, simple in maintenance but high in performance, can also find its application in 75~285 V AC input voltage.