There are so many variations on how late 90's DP's were wired.
Regarding the inverter....think of it a simply a way to provide 120 Volt A/C to your unit when the genset is not running and you are not hooked up to shore power.
There many be units like one described above, where shore power has priority over genset, or they may be like mine where genset trumps shore power.
There may be units that have designated 120V A/C receptacles that are powered only by the inverter, or units like mine where ALL 120 Volt Receptacles are powered by either the genset or shore power, except when dry camping when ALL receptacles are powered by the inverter providing it is turned ON.
Just get to know YOUR coach and all will be fine!