Summary

Made this because there so many different box sizes and formats.
Made this in Fusion360, you can change parameters to fi your needs.
UPDATE 03.09.2024 - made plug placement smarter.
Main:
Box_width - width of your box
Box_height - height of your box
Plug_quantity - how many plugs you want for your box (2 recommended, you can experiment with them, distance betveen plugs have 25mm step)
Wall_height - overall height of holder, be creative!
Other parameters are static, but you can try to change them if you need.