While carbon fiber paper (CFP) has been widely used in batteries, fuel cells, and supercapacitors, its effect on device performance can be rather complicated. In this study, we examined the effect of CFP from different batches on the performance of a CFP-supported MnOx hybrid supercapacitor (CFP/MnOx). It is found that the contribution of the MnOx to the capacitance is dominating if the MnOx coating on CFP is dense and conformal, but becomes much less significant if the MnOx coating on CFP is porous or non-conformal. This is because annealing CFP/MnOx at 400 °C in air is necessary to obtain proper MnOx phases for high capacitance; the annealing process may increase the specific surface area of CFP if it is not fully covered by MnOx. Also, the etching of carbon surface weakens the attachment of MnOx to CFP and worsens the electrical connection of MnOx to CFP, further reducing the contribution of MnOx to capacitance. Finally, much to our surprise, it is found that the properties of the CFP varied from batches to batches, which critically influence the MnOx coating morphology/density. These factors in turn greatly affect the contribution of each component to the capacitance of the CFP/MnOx hybrid supercapacitors.