This is a simple case for a LM2596 buck converter. I made it when I upgraded to silent fans on my Ender 3 V2 and installed Noctua fans and had to step down the voltage from 24V to 12V.
Edit: the top didn't fit very snugly, so I tweeked the tolerances a little bit and after reprinting it I find it fits much better now.
The author marked this model as their own original creation.