Electrochemical charge injection (ECI) is proved a powerful technique to maximize the available widen potential range of aqueous electrolyte. In this report, reduced graphene oxide/polymer dots (rGO/PDs) nanocomposites are prepared and tested as electrode materials for flexible supercapacitors. The weight ratio of GO/PDs plays an important role in the electrochemical performance of rGO/PDs nanocomposites. Through the ECI technique, a 1.7-V output potential can be delivered by rGO/PDs-based flexible supercapacitors operating with 1 mol L−1 Na2SO4 aqueous electrolyte. A specific energy of 7.1 W h kg−1 with corresponding specific power of 85 W kg−1 can be achieved for a typical flexible supercapacitor, which exhibits a capacitance retention of 90.6% after 5000 cycles at 0.5 A g−1.