This modification allows the Mellow LLL filament buffer to be powered via USB-C PD using this chip: https://www.aliexpress.us/item/3256803641829293.html. You will need to glue the USB-C PD chip to the bottom of the case and route the power wires from the USB-C PD chip through the now-unused central screw hole in the control PCB (as pictured) and solder them to the control PCB +5V and GND pins (as pictured).
The author remixed this model.
The Mellow LLL filament buffer is fantastic, but I found myself using it on filament dry boxes, which don't have 5V power supplies, so I remixed the case and buffer files to fit a USB-C PD chip. I have only uploaded the files I modified and you should get the rest from the original site.