It's a regular DC connector of the kind that is in just about all devices that is powered by a "wall wart".
Unfortunately, there's a huge amount of (combinations of) sizes, so you have to measure it up, with calipers, to at least 0.1mm precision to find the one you need.
If you have the plug, you need to measure the outer diameter of the middle pin (add about 0.2-0.3mm), as well as the inner diameter of the outer "tube" (subtract ~0.2-0.3mm) and the length of the pin (subtract ~0.5mm).
Or, if it's the socket you have, measure the outer diameter of the outer tube, the diameter of the middle "hole" and the depth of the latter.
Add and subtract as relevant, or it will be too tight and may get stuck.
You can get both plugs and sockets from Mouser
, or just use their page to check your measurements, but most shops only have a few different sizes, so ordering from Mouser might be the easy way.