It's not hard to sand and polish out the scratches; what's difficult is to match that semigloss finish of the plastic piece. The more you sand, the smoother the surface gets, which isn't going to match the finish of the surrounding plastic. It can be really hard, if not impossible, to match a finish on bare plastic that isn't a smooth high gloss. You could either sand the entire thing until not only the scratches were removed but that the finish on the whole piece was uniform, or else buy another piece like Tenman did.
You could try to mask the area around the scratches with several layers of masking tape to protect it, and confine your sanding to the smallest area possible. Don't sand all the way up to the masking tape; that'll leave a harsh demarcation between the damaged and undamaged area. I'd start sanding with something a little finer than usual, like 220 grit wet or dry paper. You probably don't want to start with any coarser grit than 220 or 320, because that just creates additional deep scratches that you have to sand away. After I followed up with 400 grit, I would try going over it with some Novus Plastic polish. If you don't sand it down to a super smooth finish (the kind you'd get with 600 grit and higher) and then go over the 400 grit sanded finish with the polish, you might come kind of close to the finish on the rest of the part. If you polish the whole part with the plastic polish, it might make an acceptable finish.
Or, one other idea; buy a piece of .080 black ABS sheet (you can get it online from hobby shops, Amazon, etc) and make a bezel for the outlet. Cut out a big plastic fender washer that the outlet fits through, and make it wide enough to cover as much of the scratched up area as possible. Cut out the bezel, sand it and polish it to make it as close as you can to the finish of the OEM plastic piece, put it over the hole in the OEM piece, then install the outlet. I'd try that solution first, since it's the least amount of work and the least risk to making the OEM part look even worse.