Supercapacitors have emerged as promising energy storage devices due to their high-power density and long cycle life, making them attractive alternatives to conventional energy storage systems. Among various electrode materials, transition metal sulfides, particularly cobalt nickel sulfides, have gained significant attention due to their superior electrical conductivity and rich redox chemistry. In this study, we synthesized cobalt nickel sulfides (CoNi₂S₄/Ni₃S₂) on nickel foam via a facile two-step hydrothermal method to investigate their electrochemical performance in two different morphologies: nanosheets and nanoarrays. Electrochemical characterization demonstrated that CoNi₂S₄/Ni₃S₂ nanoarrays exhibited enhanced performance compared to their nanosheet counterparts, with an areal specific capacitance of 8203.63 mF cm−2 at 30 mA cm−2 over 6000 cycles. The superior performance of the nanoarrays was attributed to their unique vertical alignment, providing more electroactive sites and reducing ion diffusion resistance. To further elucidate the electronic properties of CoNi₂S₄/Ni₃S₂, density functional theory (DFT) calculations were performed. The results indicated that the heterostructure exhibited an increased density of states near the Fermi level compared to pristine CoNi₂S₄, leading to improved charge storage capability. Quantum capacitance analysis revealed that the CoNi₂S₄/Ni₃S₂ heterostructure possessed higher capacitance values over a range of electrode potentials, corroborating the enhanced electrochemical properties observed experimentally. Furthermore, work function analysis suggested improved electronic conductivity in the hybrid structure, further supporting its superior charge transfer characteristics. The hybrid solid-state device fabricated by coupling of CoNi₂S₄/Ni₃S₂ electrodes with activated carbon, delivered an energy density of 0.204 mWh cm−2 at a power density of 8 mW cm−2. Impressively, even at a high-power density of 40.0 mW cm−2, it retained an areal energy density of 0.039 mWh cm−2.