ZAC ZAS power supply unit is designed for jetton automats placed in premises with frequent momentary mains failure. The failures negatively affect electronics of jetton automats and may destroy them in the upshot. In the case of mains failure output voltage is switched off for 10 seconds and then switched on again. The dangerous momentary mains failure is therefore avoided and replaced by controlled switching off and on of the jetton automat electronics, which eliminates the threat of electronics destruction.