We use a redox mediator pair - hydroquinone (for positive electrode) and sodium anthraquinone-2-sulfonate (for negative electrode) - to treat the activated carbon electrodes for fabricating asymmetric supercapacitors. This simple adsorption-based treatment improves the specific capacity of the activated carbon electrode from 69.3 mAh g(-1) to 300.4 mAh g(-1) (negative electrode) and 63.5 mAh g(-1) to 301.1 mAh g(-1) (positive electrode). The charge balance between the two electrodes is achieved by synchronous potential measurements on redox reaction of hydroquinone and anthraquinone-2-sulfonate. Under 5 A g(-1), the asymmetric supercapacitor delivers a high energy density of 37.1 Wh kg(-1) with the power density of 2087 W kg(-1). Meanwhile, the asymmetric supercapacitor demonstrates excellent cycling stability, capable of retaining 81.8% of its capacity after 20000 cycles at 10 A g(-1). A flexible solid-state asymmetric supercapacitor is fabricated with the treated electrode-pair and exhibits excellent flexing stability, high volumetric energy density (2.20 mWh cm(-3) at 0.017 W cm(-3)), and good cycling stability (> 91% capacity retention after 3000 cycles), which holds great potential for application in wearable electronics.