In this study, barnacle-like manganese oxide (MnO2) decorated porous carbon nanofibers (PCNF) were synthesized using electrospinning and the chemical precipitation method for high-performance asymmetric supercapacitors. The porous structure of PCNF was acquired using poly(styrene-co-acrylonitrile) in the electrospinning solution. In order to obtain the optimized barnacle-like MnO2 on PCNF (MnO2-PCNF), the barnacle-like MnO2 was synthesized using different synthetic times (namely, 1.5, 3.0, and 7.0 min) of the chemical precipitation. Among them, the optimized MnO2-PCNF for 3.0 min exhibited the well-dispersed MnO2 on the PCNF with the nano-size of 190-218 nm. The optimized MnO2-PCNF showed the superior specific capacitance of 209.8 F g(-1) at 10 mV s(-1) and the excellent high-rate performance of 160.3 F g(-1) at 200 mV s(-1) with the capacitance retention of 98.7% at 100 mV s(-1) for 300 cycles. In addition, electrochemical performances of asymmetric cell (constructed activated carbon and MnO2-PCNF) showed the high specific capacitance of 60.6 F g(-1) at the current density of 0.5 A g(-1), high-rate capacitance of 30.0 F g(-1) at the current density of 10 A g(-1), and the excellent energy density of 30.3-15.0 Wh kg(-1) in the power density range from 270 to 9000 W kg(-1). The enhanced electrochemical performance can be explained by the synergistic effects of barnacle-like MnO2 nanoparticles with a high active area related to high specific capacitance and well-dispersed MnO2 with a short ion diffusion length related to the excellent high-rate performance.