Its just a 5.5mm x 2.1mm barel adapter. The X3000 can accept a wide range of input voltages from 9v-36v so you can connect it to your RV’s 12v power supply.
I use this one for my X3000 in my travel trailer (no, I don’t use the included adapters), but anything similar with a 5.5x2.1 barrel adapter will work: https://www.amazon.ca/gp/aw/d/B0925ZX7V3