This paper presents flyback converter combined with single-capacitor turn-off snubber for auto-tuning fan rotational speed system. The proposed system can automatically regulate rotational speed of fan, depending on temperature in the chassis of the equipments. Its control algorithm is to regulate output voltage of the proposed converter. With this approach, the wear and tear of the bearing of fan can be reduced and the circuit structure compared with the conventional two stage driving circuit can be simplified. Therefore, the proposed system can raise conversion efficiency, reduce component count, weight and size. Moreover, in order to further increase conversion efficiency of the proposed system, a single-capacitor turn-off snubber is adopted to reduce switching loss at turn off transition, Finally, a prototype under output voltage varied from 5V~12V and maximum output power of 200W has been implemented to prove the feasibility of the proposed auto-tuning fan rotational speed system.