Summary

I designed this in Blender and it's a pretty basic design, but fairly sturdy. I had a 15 lb. weight hanging for it for several months. I think it could probably handle more. It will attach to the 1" tube of a wire shelf with the straps and a few small screws of your choice. For the shelf my plan is to just cut a piece of 3/8" plywood and screw down into the top part of the bracket, but not too far. I'll probably drill some pilot holes. You could set the infill to 100% in these areas for more strength and split resistance.

I printed this set at .2-layer height with support to handle the areas where the shelf pole will go. These are in Hatchbox black PLA. I used my old CR10S to allow printing the entre bracket at once.