<p>The swift economic growth and the explosive expansion of the portable electronics market have led to a significant demand for clean and advanced energy storage and conversion technologies. In this study, we present the synthesis of simple, eco-friendly, and cost-effective nanocomposites comprising manganese oxide (MnO), graphene nanosheets naturally derived from onion peel (OP), and carbon dots (CDs) naturally derived from radish, referred as MnO/OP and MnO/CD, respectively. These nanocomposites were synthesized through a cost-effective and eco-friendly hydrothermal approach, employing kitchen waste-derived carbonaceous materials in alignment with green chemistry principles. Morphological characterization revealed that carbon particles were uniformly decorated on the MnO surface. Electrochemical studies, including cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy were performed by using three electrode configurations. The results indicated that the MnO/CD nanocomposite exhibited highest capacitance of 812.8 Fg⁻¹ in comparison to 412.8 Fg⁻¹ capacitance of MnO/OP in 2&#xa0;M H₂SO₄ electrolyte solution at 1 Ag⁻¹ current density. The outstanding supercapacitor performance of the nanocomposite is attributed to the synergistic combination of the high electrical conductivity of carbon dots (CDs) and the exceptional mechanical stability of MnO, which serves as a robust base within the matrix. This synergy offers a sustainable and cost-effective pathway for developing high-performance materials for energy storage applications.</p>