Alto shaam
PC
Yes, they are electric. There is the cook & hold which is likely what you had, I have one of those as well, a double over/under setup, they are for used to hold things like you say, and also to cook, you can set a cook temp, a cook time, and a hold temp.
They are used as well for prime rib in the big places like Laurey's etc. They put them in the neight before and cook em low and slow. The ovens are sealed so no moisture gets out.
The smoke oven is a single, and is a bit wider and shorter, same cook and hold settings but also has a small tray w/electrode you put hardwood chips in. It does not take too much wood, as the oven is sealed. A pain to clean the smoke oven though.
The cook/hold is also great to do whole corned beef, you don't even take it out of the cryovac, there is little to no shrinkage, and it really comes out great!