An electrolyte for activating an electrolytic or electrochemical capacitor is described. The electrolyte preferably includes a mixed solvent of water and ethylene glycol having an ammonium salt dissolved therein. An acid such as phosphoric or acetic acid is used to provide a pH of about 3 to 6. The electrolyte is particularly useful for activating a ruthenium oxide/tantalum capacitor having an anode breakdown voltage in the range of 175 to 300 volts.