This paper presents the synthesis and electrochemical evaluation of nickel sulfide (NiS ₂) nanosheet encapsulated polyaniline (PANI) nanofiber nanocomposites. These nanocomposites, synthesized via chemical reflux at 70℃ in varying NiS ₂ to PANI mass ratios (1:1, 1:2, 1:3), are designated as NiP1, NiP2, and NiP3. X-ray diffraction (XRD) data reveals the greater crystallite size of NiP2 which further leads to higher surface area. Scanning electron microscopy (SEM) analysis shows that NiP2 is more porous due to well assembled morphology of NiS ₂ nanosheets over PANI nanofibers. Among the composites, the NiP2 variant demonstrates superior electrochemical performance, achieving a specific capacitance of 217.88 F g ^-1 at a current density of 1 A g ^-1 in a 2M KOH electrolyte. Further enhancing the energy density of supercapacitors for advanced applications, the structure-modulated NiP2 (positive potential electrode) is integrated with functionalized carbon nanotubes (f-CNT) as the negative potential material, extending the voltage window from 0.65 to 1.4V. The NiP2//f-CNT supercapacitor displays an energy density of 16 Wh kg ^-1 at a power density of 1318.53 W kg ^-1, maintaining 90.7% of its initial capacitance after 5000 charge-discharge cycles. These findings highlight the transformative potential of NiS ₂/PANI nanocomposites, leveraging the synergistic effects between NiS ₂ and PANI to significantly enhance ion transport and charge storage capabilities, thus providing a viable solution to the shortcomings of conventional supercapacitor electrodes.