This work presents a novel porous activated carbon electrode based on quinoa straw (QSC), which is derived from the Qinghai-Tibet Plateau. The QSC is prepared through simple precarbonization and potassium carbonate (K2CO3) activation processes and is intended for use in supercapacitors. The QSC-3 exhibits a high specific capacitance of 469.5 F g-1 at a current density of 0.5 A g-1, as well as a high specific surface area of 1802 m2 g-1. Additionally, symmetrical supercapacitors assembled using QSC-3 samples demonstrate a superior energy power density. In a 3 M KOH electrolyte, the energy density can reach 15.0 Wh kg-1 at a power density of 689.7 W kg-1. In a 1 M Na2SO4 electrolyte, the power density reaches 999.00 W kg-1, and the energy density is 39.68 Wh kg-1. Furthermore, the device shows excellent cycle life in both 3 M KOH and 1 M Na2SO4 electrolytes, with capacitance retentions of 97.55% and 96.20% after 10 000 cycles, respectively. This study provides an excellent example of utilizing waste quinoa straw to achieve low-cost, high-performance supercapacitor electrode material for sustainable electrochemical energy storage systems.