Anet changed the default A6 power supply around the beginning of 2018. The STL has been modified to accommodate the change, and still work for pre-2018 printers. (i.e. some internal features were removed, and the screw hole over the receptacle was elongated slightly.)
Use "A6PowerCover2018-R1.stl" for any year, factory-shipped, power supply.
(For archival purposes, or should you have a pre-2018 printer and prefer to use the original design, use "A6PowerCover-pre2018.stl")
I liked the basic cover by MaqsYo. Simple and only required a single screw (a 3mm A6 spare) to hold it in place. However, I was really looking for a cover with power cable receptacle and switch. So I bumped out the shape and added the receptacle. I also tweaked a number of other things for ease of installation, cooling, printing, etc.
There is a small support section you need to break-off once it's printed (so you can get it past the servo cable). You'll need to drill the two mounting holes for the receptacle/switch. Be careful if you plan to attach it with screws (as opposed using a thru-bolt with a nut). If you drill too small of a pilot hole, you can crack the print when you drive the screw in.
I purchased the receptacle/switch at Amazon for about $6, which included the crimp connectors for it.
Do not try to solder the wires directly to the receptacle/switch tabs. Use the crimp connectors. For the interconnecting wires, take some out of the original A6 power cable (which you will no longer be using). You also need a standard tower/desktop PC power cable. Most people have at least one lying around somewhere unused. If not, ask your neighbor. The way I wired it, the switch always glows, not just when it's "on". I assume there is a way to wire it so it only glows when it's "on", but I did not investigate that.
I printed it without support and it came out pretty good. I got a little bit of a wave along one of the sides, and a bit of stringing on the vent slots, but I'm enough happy with it.
You can print with lower resolution. I experimented a bit and was happiest with 0.15. In some ways, 0.4 worked better, but the walls seemed more prone to splitting. The bridging in the cutout for the receptacle worked fine for me, but your mileage may vary. If you're having problems, try using some supports.