I did a lot of research trying to find this product and this is what I found. Ring says that it does not make an extension cable and does not support/reccomend this cable, but I bought it anyway and it works fine! I bought 2 of these cables at $4.55 USD each and extended the original Solar Panel cable 20 extra feet for a total length of 33 feet and I have had no problems. The included solar panel DC cable length is 13-ft. (3.96-m.) with a weatherproof barrel connector manufactured by Wasserstein. I can’t recall the item/part number, but if you do a search on the description below, you should be able to find it.
DC Power (3.5mm x 1.35mm) Male to Female Camera Extension Adapter Cable 10FT (White or Black)
Manufacturer: Wasserstein
Type: DC Power Connector
Cable Length: 10 ft.
Connector A (Male): Coaxial DC Power (3.5x1.35mm)
Connector B (Female): Coaxial DC Power (3.5x1.35mm)
Model: DC Cable
By the way, Ring Support couldn’t tell me the size of the barrel connectors (they have to be 3.5x1.35mm (Male - Female). Hope this helps!!!