In this paper, we offer new porous activated carbons (PACs) made from waste Argan pulp for use in solid-state supercapacitors. The synthesis is a two-step process of carbonization and KOH activation, with temperatures ranging from 700 to 850 °C and ratios ranging from 1:3 to 1:4. The carbon material obtained exhibits a significant surface area ranging from 2757 to 3235 m2 g−1. The evaluation of electrochemical characteristics in a two-electrode system using a 1 M H2SO4 electrolyte reveals exceptional capacitance and specific energy when subjected to a current density of 125 mAg-1. The AP-800-3 has outstanding performance, with a specific capacitance of 460 F g−1 and a specific energy of 15.98 Wh kg−1. Significantly, this particular PAC has exceptional durability in cycling, as it maintains its full specific capacitance even after undergoing 2500 charge and discharge cycles at a rate of 1 A.g−1. When testing with 6 M KOH and 1 M Na2SO4 electrolytes, the capacitance is found to be lower compared to 1 M H2SO4 (239 F g−1 and 258 F g−1, respectively). The superior performance in 1 M H2SO4 emphasizes the interplay between electrolyte composition, porosity, and appropriate microstructure of the PACs. This study proposes eco-friendly method for selecting supercapacitor electrode materials.