An oxygen plasma process for treating a dielectric oxide layer, particularly an anodic oxide, subsequent to its incorporation into an electrolytic capacitor is described. The present treatment reduces DC leakage and improves shelf life stability of the resulting capacitor in comparison to anodic oxides treated in a conventional manner. This is important for critical applications such as implantable cardioverter defibrillators where capacitor charging time and charge/discharge energy efficiency are critical.