Our Outback has 3 slides: Bedroom closet, drivers side long slide, passenger side (front) short slide. The longest slide does not have electric plugs. The short one does.
The wire running from the main body of the trailer to the slide is supported on a plastic support that reminds me of a an oversize wide hot wheels track on it's side. The electric wire is attached to it. When the slide retracts or extends, the plastic (track) bend with the slide, in or out, thus keeping the wire from kinking and getting caught on moving parts. I check it often to make sure it hasn't come loose. If that plastic support ever came loose, I think it would become a tangled mess very quick when the slides move.
The longer slide does not have plugs. Too bad, because we swapped furniture around, ended up getting rid of 2 rocker chairs and the free standing table and chairs and replaced with a house-hold recliner sofa. I miss the plugs as we like to use electronics a lot in that spot. We end up running extension cords. At both ends (in the main trailer) are plugs, but it does require running extension cords. Someday I may rig up a more permanent set of plugs in the long slide, but it's not happening today.