u/Bare-Minimum-Energy

Hello everyone. So, this is my plan. I want to plug in the power cord of the echo show 15 in the roof and bring that cable down to the echo show 15 rather than putting a massive hole in my wall which will be a hassle to fix up later if I ever have to. My issue is that I either need an extension cable for the DC wire or I can simply bring the wire down from the roof and it will reach it. Here are my questions:

1. How long is the power cable that comes with the Echo Show 15?
2. What do I need to look for when buying an extension cable? Eg: barrel size, voltage, etc.
3. Do you have any links that could be shared that could come in handy with this?

Thanks for your help.