Can you dual output an alternator ?

No you cannot dual output an automotive alternator, you can however install a 110 AC alternator on your engine. You will need to have brackets manufactured and a separate belt drive system. Be aware that these alternators use a lot of engine horsepower to run a load and they are specialized alternators so they can run at varying engine speeds so they are not like a stand alone generator unit.

Best and Safest way (in my and ONLY opinion) to be protected from or not exposed to danger or risk: Install another same rate battery on parallel to double the CA (with the battery you already have) on any suitable place in your Car/Van connected to a Power Inverter with a Breaker fuse. Look for Electrical Specialist advice IF in doubt, feeling of uncertainty or lack of conviction,Information, and skills . Thanks

AC is rectified into DC , Transformers step voltages up or down ,It's O.K. even Jeopardy got that one wrong , A cars alternator won't produce any voltage unless some power is supplied to it's coils from the regulator