NiO has been intensively studied as a promising electrode material for supercapacitors because of its high theoretical specific capacitance, well-defined redox behavior, and good chemical compatibility with nickel foam. However, it still suffers from inferior rate capability and cycling stability because of the simple component and random structural integration. Herein, we report a tunable sulfuration process of NiO nanosheets constructed on porous nickel foam for supercapacitor applications. The resulting NiO/Ni₃S₂ with distinct structural features exhibits an ultra-high specific capacitance of 2153 F g⁻¹ at a current density of 1 A g⁻¹, and the capacitance is retained at 1169 F g⁻¹ even at a current density as high as 30 A g⁻¹. An asymmetric supercapacitor device fabricated with NiO/Ni₃S₂ as the positive electrode and activated carbon as the negative electrode delivers high energy and power densities (52.9 W h kg⁻¹ at 1.6 kW kg⁻¹; 26.3 W h kg⁻¹ at 6.4 kW kg⁻¹), and good cycling stability (a capacitance retention of 92.9% over 5000 cycles).