Activated porous carbons containing both micropores and meso-/macropores are prepared by cost-effective pyrolysis carbonization and the subsequent alkali activation of a easily available biomass, paulownia flower (PF). The as-prepared activated PF carbons (a-PFCs) show high specific surface areas, suitable pore size distributions, superhydrophilicity and partial graphitization phase, all of which are essential for achieving high electrochemical performances as supercapacitor electrodes. The symmetric supercapacitor based on a-PFC3, which is synthesized at the mass ratio of KOH to PF derived carbon (PFC) to be 3 during activation step, offers a specific capacitance of 297Fg−1 at current density of 1Ag−1 within potential range of #2–3#1V using 1M H2SO4 electrolyte. Owing to the high specific capacitance and wide potential window, the supercapacitor delivers high energy densities of 44.5∼22.2Whkg−1 under the power outputs of 247∼3781Wkg−1. The high specific capacitance, good rate capability, superior cycling reliability and excellent capacitance maintaining ability in tandem cell group make the a-PFC3 supercapacitor a competitive unit in assembling of amplified tandem battery pack.