That's a Winegard 7542 TV amplifier. Actually, it's the power supply and power switch for the system. The actual amplifier is in the TV antenna located on the roof. You turn it on to watch over the air (OTA) channels and turn it off to watch cable/satellite channels.
Here's one place to purchase a replacement:
https://www.amazon.com/Winegard-RV-7...H7DB3A8ZZ0BMJ6
You should have a owner's manual for it in the trailer information packet, if you don't, you can download one here:
https://manuals.solidsignal.com/2451233.pdf
The Winegard system has a 2 year warranty, so depending on when you purchased your trailer, it may still be covered by the Winegard warranty. Keystone won't help you with the claim, but your dealer "should" or you can contact Winegard on your own.