This is nothing special, just a basic bracket to use in a pinch but is surprisingly strong. I printed mine with 6 walls and 35% infill and have been using 2 of them to hold a wooden shelf with up to 11 rolls of filament at any one time.

Make sure you use the appropriate wall anchor to mount this to your wall, I used 4 drywall anchors which can support up to 20kg each but you will need to check what you need for your own walls.

Prints without supports, simple but effective.