Carbon nanofibers incorporated with other carbon additives, i.e. acetylene black (ACB), hollow carbon sphere (HCS), and reduced graphene oxide sheets (rGO), were successfully produced by an electrospinning process. The influence of carbon additives was evaluated through the electrochemical performance of carbon-based nanofiber supercapacitors. The carbon additives with high sp(2) content not only enhanced specific surface area but also improved electrical conductivity of the carbon nanofibers. A finely tuned 1 wt % ACB loaded to the carbon nanofibers provided a specific surface area of 116 m(2) g(-1), a specific capacitance of 209 F g(-1) at 2 mA per cell, a specific energy of 14.2 Wh kg(-1), a maximum specific power of 8.3 kW kg(-1), and >99% capacity retention over 10 000 cycles in 1 M H2SO4 aqueous electrolyte. The carbon fiber composites here may be practically used in supercapacitors.