Total Power for the 12v system for Gen 5 (Normal/AWD)

I believe you're talking here about an inverter supplied in the 2023 Prime that produces 120 Vrms AC for your use. I am pretty sure that inverter draws power directly from the car's high-voltage electrical system (as people with older-generation Prii have occasionally done aftermarket). So its 1500 W rating is real, and does not depend on the car's 12 VDC system.

Do you still have a question about the 12 VDC system capacity anyway, or does the above answer the question you had?

 

The DC/DC converter producing 12 volts has typically had a rating around 120 amps (that's the published gen 3 figure), or 1440 watts at 12 volts, 1700 watts at 14.2.

To figure how much of that you can use, you have to account for how much the car uses. I don't have gen 5 figures specifically, but from past gens you can sort of expect the car to use anywhere from around 400 watts (leaving more than a thousand for you) if the car is just READY with most of its own electrical accessories turned off, to using up pretty much the whole DC/DC converter capacity and leaving not much at all for you, when several of the higher-power loads in the car are being used. So if you're planning a heavy added load, you kind of have to be aware that it might be ok at some times but not other times.

 

Wouldn't you be best off running a mains-powered charger from one of the mains outlets? You will always get 1500W there.