The introduction of pillared agents or dopants to the graphene used as the electroactive material in supercapacitor electrodes can be an efficient way to facilitate ion transfer, mitigate re-stacking, and improve electrochemical performance. We evaluated the effect of different precursors containing nitrogen (N) and sulfur (S) atoms to dope graphene flake (GF) lattices. The electrochemical performance of the doped GF was assessed in 1 M KOH and 1 M Na2SO4 electrolytes. N- and S-doped GF flakes were synthesized via mechanochemical synthesis, also known as ball milling. After being ground, the materials were calcined under N2. The physicochemical characterization of the materials evidenced the co-doping of both S and N into the graphene backbone, as corroborated by the results of Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). As shown by the results, the nature of the precursors influences the ratio of S and N in the doped graphene flakes and, consequently, the response of the electroactive electrode material. The co-doping obtained using 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole revealed a specific capacitance of 48 F.g−1 at 1.0 A∙g−1 and over 90% capacitance retention after 10,000 cycles at 10.0 A∙g−1 in Na2SO4.