Sorry for the typo error. The system and MCB should be apart from each other. And answer to your question that I haven't tried it in another circuit.
You'll have to in order to determine where the problem is. You should also identify what else is connected to the same circuit. Set the circuit breaker to OFF or make it trip and don't reset it. Then find another outlet that still has power and is therefore on a different circuit. If that breaker doesn't trip, then you know that something else is on the other circuit or the breaker no longer works properly. If both breakers trip, then RMA the PSU.