There are many devices. Most of them contain MOVs (metal Oxcide Varisistors) which offer some SPIKE (not surge) suppression. These inclued the common six outlet (or smaller) "Surge Guards" sold in supermarkets, office supply and department stores from here to there and back again. IF a true surge hits these pupplies make like firecrackers (I kid you now I was there when it happened and that is exactly what they sounded like).
Autoformers and EMS systems may well contain them, Some Auto Transfer Switches contain them.. but in the event of a true surge,, See "Firecracker" above.
The primary job of the EMS is to limit the current draw when on less than 50 amps, IF it sees demand for more than say 25 amps (on 30) 1r 15 (on 20) it will shed a load or two to keep it down. This "Protects" you from having to get dressed, go outside and reset the )(*@#&$)@#* Circuit breaker.
The job of the Autoformer or automatic boost transformer is to protect you against brown out of other causes of low voltage, It does this by kicking in and boosting the voltage, at least one make will also buck a high voltage.
The RV-Surge Guard devices, are better called a power line guard or protector monitor, usually, frequency and voltage, if one (or both) of them are too high, or too low it cuts power to your RV cause NONE is better than BAD. Thus protecting the stuff that is voltage senistive. This is a TRUE surge guard because heaven forbid the power company screw up on you as they did on me and hit you with way more than 120vac.. IT will shut you down, hopefully before damage happens.
The power chain
By the way, that way if the voltage goes low the autoformer can boost it before the surge guard kills it. And if the autoformer gets "Stuck" in boost, the surge guard will kill that too.
Home is where I park it!