Heres a basic case I made for a cheap USBC PD Decoy Board, very cheap on Aliexpress. I'll add a pic of the one I used and also post a Aliexpress link. It supports 9, 12, 15 and 20v, although not super easy to change between as you have to move a very small resistor. They all seem to be preconfigured to 12v.

I tried to keep it as slim as possible but make the case so it can snap together and stay together. Theres also some strain relief for the cable, it wont stand up to a big tug tho! you could always hotglue as well.

I designed it around a cable I intended to use which had a diameter of 3.3mm, if your cable to thinner then the strain relief wont work too well, if your cable is thicker then you may need to file down a little!

I also added some text for the different voltages, these are saved as 3mf files but ofcourse theres a blank one. The Base is the same for all.

https://www.aliexpress.com/item/1005006191468955.html