It has been a challenging task for organic electronic devices to control and convert electric power due to their vulnerability when exposed to high voltages. In this work, the design, fabrication, and applications of AC-DC and DC-AC organic power converters based on high-voltage organic thin-film transistors are presented. The organic AC-DC converters, comprising diode-configured high voltage organic thin-film transistors as the rectifying unit, is capable of transforming a high AC input voltage to a selectable DC voltage. On the contrary, the organic DC-AC converter, using an astable multivibrator as oscillation generator, is capable of converting a high DC voltage to a high AC voltage as a power inverter. The functionality of the organic AC-DC power converter is demonstrated through charging supercapacitors as a quasi-constant current supply and, in addition, the successful driving of organic light-emitting devices to high luminescence and efficiency. Expanding the application of organic thin-film transistors into power conversion paves the road towards organic power electronics for cost-efficient and Eco-friendly power electronics in the future.