There are now 3 options for RV fridges.
1: Traditional "Absorption cooling units" I will assume you know how they work, When running on electric they genrally suck around 350-400 watts. Or they can run on Propane.. This is better when you have limited power.
2: High Effiency Compressor Units, both Dometic and Norcold have at least one model, of RV fridge, plus at least one model of chest freezer/fridge. I have an ENGEL Chest freezer or fridge here (Adjustable cold) These draw around 35-40 watts, yes, less than a single double bulb incandescent light fixture.
3: Residential, usually 100-350 watts depending on size and age, these require you have an INVERTER (True sine is best) and enough battery to support if dry camping.. Runnign down the road hopefully the alternator can provide, but it puts a fairly good size load on the alternator..
To figure out what a residential take get a KILL-A-WATT meter, this is about a kill-a-buck worth of test gear in a 20 dollar (or less) Box. Plug in your fridge at home and take a look.. When the compresser is runnign see how many amps it takes,, Multiply by 11 for your battery (YES 11, inverter is only 90% efficient at best) that is what the alternator has to push to the batteries.. Note the KWH after 24 hours, that's how much power was supplied to it .. Each KWH is 100 amp hours