Due to industrial requirements for energy as well as environmental problems related to the use of fossil fuels, the supercapacitor has been the suitable alternative. Hence, in this study, the new nanocomposite was synthesized from polyethylene glycol diacid (COOH-PEG-COOH), cobalt (II) acetate tetrahydrate (Co (OAc)₂) by using the one-step method. In this method, the polyethylene glycol diacid forms polymer dots (PDs), is simultaneously composited with Co (OAc)₂, and form the PDs-CoO nanocomposite. The new PDs-CoO nanocomposite was fully identified by various techniques. To accurately investigate the electrochemical performance, the PDs-CoO nanocomposite symmetric supercapacitor and cobalt (II) acetate tetrahydrate symmetric supercapacitor were fabricated. The PDs-CoO nanocomposite supercapacitor has excellent electrical conductivity. Specific pseudocapacitance was calculated by the cyclic voltammetry (CV) and impedance (EIS) techniques. In all electrochemical methods, the specific pseudcapacitance of the nanocomposite is about five times higher than that of cobalt (II) acetate tetrahydrate due to the presence of the PDs. The PDs-CoO nanocomposite supercapacitor has a high specific pseudocapacitance, about 1020 F.g⁻¹ at 1 A.g⁻¹ current density, and very well cyclic stability of 98.7% capacitance retention over 10,000 cyclic voltammetry cycles at 1 A.g⁻¹. Also, a low power system was designed to test the actual performance of the supercapacitor, which confirmed the results of the CV, charge/discharge (GCD), and EIS.