Most of the better "battery chargers" are also "power supplies". Iota and Samlex both say in their brochures that they can be used as power supplies.
My little Norcold 323 says on the sticker that it uses 11.7a running on 12v - so I'd say any decent MULTI-stage (so it eventually goes to float and doesn't overcharge the battery) charger hooked up to shore power should not only supply enough power, but also might just keep your battery topped up at the same time - as long as it is rated to supply at least however much your fridge draws.
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Current: 76 E-250, bubble-top, self-contained|couple of old Yamaha enduros
Previous wheelers: 41 Willys|78 FJ40|78 Bronco|84 Bronco|74 Ramcharger|78 Ramcharger|79 D150 PowerWagon|77 D100|79 D400 dually, converted to 4WD, utility bed, 10' Lance|75 Westy|69 Scout, RHD|bunch of others|bunch of bikes|couple of boats|couple of motorhomes|blah blah|so what|not my idea|just doin' what I'm told|wank wank|this space for rent|candy is dandy|but liquor is quicker