The rapidly developing electronics industry is producing miniaturized electronic devices with flexible, portable and wearable characteristics, requiring high-performance miniature energy storage devices with flexible and light weight properties. Herein, we have successfully fabricated highly porous, binder free three-dimensional flower-like NiCo₂O₄/Ni nanostructures on Ni-wire as a fiber electrode for high-performance flexible fiber supercapacitors. Such a unique structure exhibited remarkable electrochemical performance with high capacitance (29.7 F cm⁻³ at 2.5 mA), excellent rate capability (97.5% retention at 20 mA), and super cycling stability (80% retention, even after 5000 cycles). The remarkable electrochemical performance is attributed to the large active area in the 3D porous architecture and direct contact between the active materials and 3D-Ni current collectors, which facilitate easy ionic/electronic transport. The symmetric fiber supercapacitor showed a gravimetric energy density of 2.18 W h kg⁻¹ (0.21 mW h cm⁻³) and a power density of 21.6 W kg⁻¹ (2.1 mW cm⁻³) with good flexibility and cycling performance, signifying potential applications in high-performance flexible energy storage devices. Further, performance in a self-powered system was demonstrated by charging these wire type NiCo₂O₄/Ni supercapacitors by serially wound DSSCs to drive commercial LEDs. These results suggest that the fabricated device has excellent potential as a power source for flexible, portable and wearable applications as well as self-powered systems.