To construct novel multicomponent transition metal oxides with the synergistic effect is always the most important strategy to improve the electrochemical performance of supercapacitor electrode materials. Here, a new type of parallelogram-like NH4CoPO4 · H2O/Ni3(PO4)2 · 8H2O/MnO2 (NNM) composites were successfully prepared by a simple hydrothermal method, and the addition amount of MnO2 was adjusted in detail. The morphology, structure, composition, particle size, and distribution of the electrode were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), Raman spectrum, and laser particle size analyzer. The results showed that when MnO2 was added at 9.7 wt%, the resulting NNM-9.7 composite exhibited a parallelogram-like morphology with an average length, width. and thickness of 5, 3, and 0.2 µm, respectively. The results of cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS) show that the NNM-9.7 electrode has large specific surface area, good conductivity, and abundant porosity, which makes it to have high-specific capacity (1180 F g−1, 1 A g−1) and excellent rate retention (980 F g−1, 10 A g−1) when compared with other electrodes, which is better than most reported electrodes of nickel–cobalt oxides/hydroxides. These results indicate that the novel NNM-9.7 composite with parallelogram-like shape and its synthesis method may provide a feasible solution for supercapacitors' material issues.