Dual Generators (not dual fuel, but two generators)

the 3k Generators have a larger gas tank and can offer a run time on heavy loads that is longer than (2) engines with smaller tanks, sharing the load

all brands inverter generators
use an Alternator at high voltage, to get high voltage DC
which is then put thru the inverter circuit to create 120v AC
the specifics of the alternator and inverter circuits vary by MFG
with everybody 'protecting' their patent design