The electrochemical performance for energy storage of a three-dimensional (3D) self-supported heterogeneous NiSex cubic-orthorhombic nanocrystals grown by a facile one-step chemical vapour deposition (CVD) approach on Ni foam substrates has been explored. The NiSex shows high specific capacitance of 1333 Fg-1 with, ultra-high energy (105 Wh kg-1) and power density (54 kW kg-1). Further by integrating the as grown NiSex as anode and reduced graphene oxide as cathode, a hybrid supercapacitor (HSC) prototype in coin cell configuration has been fabricated. The device shows better capacitance (40 F g−1) with high energy (22 Wh kg−1) and power density (5.8 kW kg−1) with robust cyclic durability (~88% capacitance retention after 10000 repeated cycles). For practical reliability of the as fabricated HSC, a red LED has been lightened by connecting with two charged coin cells. These outstanding performances of the HSC proves to be the promising one for applications in high energy storage systems.