Is this a 110volt external plug?

Any ideas on what this is? I am guessing it is for plugging the van into a 110volt outlet. Would I be able to swap this to a standard two prong female outlet or find an adapter?

The grey thing in the 4th photo says “External Input” on the hand printed label and the spec label says 250V. That’s not 110V.

Ah in the 3rd photo the other label on the rhs of that grey thing says “Inverter”.

I presume this is a fresh import from Japan to the US?
You should not use it. Japan voltage is 100v (50Hz/60Hz). So a little confusing why this transformer is outputting 250v.... why would it be stepping up the voltage?
There is also likely state mandate for such electrical ports to be certified. Check your states requirement. Place like Australia/New Zealand have mandates for certification.

It looks like a European two pin. Which would be 240 v at 50Hz. Abandon it.

Japan uses 200V for caravan and high power appliances, splitting the 100V phase like the USA does. Most associated circuits and components seem to be rated for 250V. Not sure the technicalities of that. There could well be step-down/conversion to both 100VAC and 12VDC somewhere in that van’s setup.

There’s no reason you shouldn’t be able to bypass that 200-100V stepdown and remove the 200V parts. Well, apart from the reason of not knowing what you’re doing. There’s electrocution involved.