Hi there, according to the manual, the AC200max has 2 inputs. One is used for multi purpose MPPT (PV, Car etc…) the other is used for a specific DC voltage from the AC adapter.
So you can split the XT90 into 2 to make it easier to plug in whatever you need into the multi-purpose port. However, you need to make sure you only ever plug in one charging source at a time to that split, as otherwise the sources would be connected together and your sources will fight with ugly results.
Solar - stationary
Shore 110v - when necessary
Chassis Battery - while driving
The DC to DC would provide a regulated 12v supply with 40a max to charge the AC200 - this would be at a much higher rate than the regular supplied 12v plug at 100w -
I have now decided against this setup as the max input is 15a to the AC200Max and limited input options - so I will use the 12v lighter plug only for now and see if this works in my environment sufficiently
Since that Renogy charger as virtually the same output voltage as your vehicle’s alternator (i.e. ~14V), feeding the MPPT device directly from your vehicle and feeding it through the Renogy should produce identical results.
In both cases, the voltage presented at the MPPT input will be ~14V (assuming you have adequately sized wiring) and the current flowing into the MPPT input will be determined by the MPPT device. In both cases, the power delivered to the Bluetti will be approximately 14V x 15A = 210 Watts.
To get a higher DC2DC charging rate, you must raise the voltage supplied to the MPPT controller, using a device that converts the vehicle’s ~14V input to a higher voltage in the MPPTs specification range (10V to 145V). Such a device, often called a “DC to DC converter”, has been discussed by Scott-Benson several times in these forums.