All-solid-state supercapacitors (SCs) were fabricated using a polyvinylidene fluoride (PVDF)/lithium trifluoromethanesulfonate (LiTFS) membrane as the separator and poly(ethylene oxide) (PEO)/lithium perchlorate (LiClO4) as the polymer electrolyte in the porous carbon electrodes. Two types of mediators, NaI/I2 and K3Fe(CN)6/K4Fe(CN)6, were added into the PEO/LiClO4 polymer electrolyte that was used to fabricate the electrodes. The voltage window in which the SCs operated was 2.5–3V. The results of electrochemical measurements, including cyclic voltammetry and galvanostatic charge/discharge, indicated that NaI/I2-containing and K3Fe(CN)6/K4Fe(CN)6-containing SCs yielded high specific capacitances of 209.0 and 138.8Fg−1, respectively. In addition to high specific capacitances for the two mediator-containing SCs, both SCs delivered high specific energies (49.1Whkg−1 at 1.6kWkg−1 for the NaI/I2-containing SC and 33.6Whkg−1 at 1.3kWkg−1 for the K3Fe(CN)6/K4Fe(CN)6-containing SC) due to the wide voltage window and fast redox reactions between mediators.