If you can't get an adapter with correct polarity you'll have to resolder the connector by cutting the wire and switching the poles. I know that switchable adapters are no choice in this case because there is not enough space around the jack on the piano, which is a pity.
If you can't get an adapter with correct polarity you'll have to resolder the connector by cutting the wire and switching the poles. I know that switchable adapters are no choice in this case because there is not enough space around the jack on the piano, which is a pity.