I doubt your alternator is told by the voltager regulator to maintain a constant 14.4volts.
Usually the 14.4v 'sought' is brief, and the voltage regulator is then dropping things into the mid to high 13s. What dictates the voltage regulator's choice of voltage is different on different makes/models/ and rigs. The length of wiring and its thickness to the house battery then affects the amount of voltage drop and the voltage reaching the battery terminals, and the battery then accepts what it wants at the voltage reaching the battery terminals, which can be quite different than the voltage at the alternator output stud.
About 1/2 to 1/3 the amps will flow into a less than fully charged battery at 13.7v, compared to 14.7v reaching the battery terminals. It depends on battery resistance, but in general the newer and healthier the battery the more amperage it will accept at that voltage.
The DC to DC chargers are intended to keep voltage at the house battery terminals in the 14.4v range after the vehicles voltage regulator says 13.7v is fine and dandy for the engine starting battery.
The solar charge controller's are generally taking 17 volts and trying to keep the battery at one of 3 voltage 'stages'.
So they are not a voltage booster, more of a voltage bucker, while the DC to DC products one hooks to the alternator are primarily boosting voltage for faster charging of house batteries. Though they can of course do the opposite too.
My Vehicle either chose 14.9v or 13.7v with little regard to logic or battery state of charge. It almost always started at 14.9v and after a few minutes would drop to 13.7v, kind of infuriating when teh battery was still well less than fully charged. Randomly it would occassionally choose other voltages, and I was never able to find any reason why it chose the voltages it did.
I had to trick my engine computer, where the stock voltage regulator resides, I then used an external voltage regulator which had an internal 2k ohm voltage adjustment potentiometer. I clipped the legs to this internal potentiometer, soldered wires to them, ran these wires to a 10 turn 2K ohm bourns potentiometer located on my dashboard next to voltmeters whose voltage sense leads are on teh batteries themselves.
With a thick copper circuit I have seen as much as 108 amps flowing into my well depleted battery from my 120 amp externally regulated alternator at 2200+ engine rpm. 12.2 amps are required to run my ignition and fuel pump at 2K rpm.
I generally choose 14.7v or 13.7v depending on temperature and how many amps the battery is accepting.
This voltage regulator modification was largely possible due to the knowledge and products Mexicowanderer shared with me, the one exception as that tricking the engine computer into believing it was still connected to the alternator, thus not illuminating the check engine light and causing the engine computer to not read the sensors and adjust fuel air mix and spark timing, required a 50 watt 10 Ohm resistor, was figured out by someone else.
Basically if I have the rpm I can almost always charge my battery as fast as safely possible whenever I drive, and this is awesome, but it requires that I am there to lower voltage once the battery is indeed full.
I can also overheat my alternator maxing it out under 25mph, but at highway speeds I can max it out and never approach dangerous alternator temps.
Improving your house battery charging via alternator can be improved with thicker wire from alternator to house battery and back, but if the voltage the alternator is told to seek is only in the high 13's, then much less charging will occur.
Influencing/ tricking the alternator's voltage regulator is possible on many vehicles, but it depends on the vehicle and its alternator.
The DC to DC chargers can take that 13,6v and boost it to 14.4 at house battery.
One can run an inverter connected to engine battery, feeding an AC powered charger onto house batteries while driving, though this can deplete starting battery to feed house battery depending on a few factors.
Essentially the Renogy or sterling or C-tek products intended to better recharge secondary batteries from an alternator, are DC Buck/Boost converters.
Here is a 300 watt buck boost converter for ~14$
https://www.amazon.com/Nicknocks-Converter-Step-up-Step-Down-Adjustable/dp/B07PFDKKTF/ref=sr_1_28?keywords=Buck+Boost+Converter&qid=1560732243&s=electronics&sr=1-28I have a 60 watt buck/boost converter I use on a 24v fan to control its speed/airflow from 7.75 to 30 volts which draws about 25 watts at 30 volts. No experience with linked product or using it for battery charging.
