[en] Graphical abstract: MnO₂-RuO₂@GNR shows enhanced capacitive performance in symmetric and asymmetric assembly with GNR resulting in high ED and PD. - Highlights: • MnO₂-RuO₂ nanoflakes are successfully synthesized on reduced graphene oxide nanoribbon (MnO₂-RuO₂@GNR). • MnO₂-RuO₂@GNR shows superior electrochemical properties in symmetric and asymmetric supercapacitor assembly. • Interconnected MnO₂-RuO₂ nanoflakes via GNR provides conducting network with enhanced diffusion kinetics. • Asymmetric supercapacitor reveals energy density 60 Wh/kg at power density 14 kW/kg with ultra-short relaxation time. - Abstract: This paper reports the interaction of 3d-4d transition metal mixed oxide as simultaneous existence of M(3d) and M(4d) expectedly enhance the electrochemical performance of the resulting composite. Electrochemical performance of MnO₂-RuO₂ nanoflakes reduced graphene oxide nanoribbon composite (MnO₂-RuO₂@GNR) is intensively explored in symmetric and asymmetric supercapacitor assembly. In situ incorporation of graphene oxide nanoribbon (GONR) during synthesis provides efficient binding sites for growth of MnO₂-RuO₂ nanoflakes via their surface functionalities. The interconnected MnO₂-RuO₂ nanoflakes via GNR form a network with enhanced diffusion kinetics leading to efficient supercapacitor performance. Fabricated asymmetric supercapacitor reveals energy density 60 Wh kg⁻¹ at power density 14 kW kg⁻¹. Based on the analysis of impedance data in terms of complex power, quick response time of supercapacitor reveals excellent power delivery of the device. Improved cycling stability after 7000 charge discharge cycles for symmetric and asymmetric supercapacitor highlights the buffering action of GNR and can be generalized for next generation high performance supercapacitor.