To enforce the interactions between polyaniline (PANI) and graphene, a facile strategy is developed in this work to fabricate the strongly coupled hybrids of PANI nanofibers and graphene (named as PAGs) by introducing different diamines to functionalize graphene oxide. As the electrode material in a two-electrode supercapacitor (SC), the ethylenediamine-functionalized hybrid (PAG-EDA) deliveries an excellent volumetric specific capacitance of 810 F cm⁻³ at 5 mV s⁻¹. The SC also manifests high cycling stability by maintaining 84.4% of the initial capacitance after 10,000 cycles. More importantly, PAG-EDA renders the SC to have both high energy density (92.15 W h kg⁻¹) and high power density (182.28 kW kg⁻¹), superior to most of the previously reported PANI based SC electrode materials.