So I ordered Multiplus-ii 12/300/120 with 3 wire terminals. My RV is 30a shore power with an onboard generator. I read in the manual that the Multiplus-II has power assist, and the AC out 1 is rated for 50a. But most 50a is 240v, so I wanted to come on here to make sure that the multiplus-ii puts out 120v on power assist so I could run this to my panel with new wiring and a new panel (rated for 50a) while on 30a shore.
Assuming you mean this 120V inverter (12/3000 model):
This is a 120V inverter and that’s what it puts out.
If you enable PowerAssist, you will be able to add the power from the inverter to the shore power to reach 50A max. Be sure to use AWG 6 or AWG 4 wire on the output to your panel, as described in the manual.
Wow I guess coffee hasn’t kicked in yet. 
Well just was talking to electrician and he was arguing about it that it would be 240v being 50a. Next time I’ll drink coffee then post 
While it is true that most (but not all) 50A shore power for RV’s is 120/240V, that doesn’t have anything to do with the voltage provided by this inverter, which 120V.
PowerAssist works by matching the phase of the incoming power, and then adding the necessary additional power when the loads exceed a limit. I recommend having PowerAssist kick in at around 25A.
If your rv is wired with a 30a shore power (single phase 120v) than yes the single phase 120v multiplus is the unit you need.
If you have a 50a shore power (split phase 2x50a 120v/ 50a240v) you would need a pair of single phase multiplus’s if you want to invert both phases (or use a 240v appliance if equipped) or a multiplus 2x120 which can pass through both shore power legs, but only inverts L1
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Yeah, that is what I was planning on putting the PowerAssist on at around probably closer to 28a. I just wanted to have the extra buffer in case the wife is cooking with the crock pot, running the AC, using the Microwave, and using the hair dryer
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