This contains the required files and a tutorial for the installation of OS X 10.15 DP on the Dell XPS 15 9550. The files and tutorials for 10.11, 10.12, 10.13 and 10.14 are in a different branch
Setup tested with the XPS15 containing Toshiba 512GB SSD, 16GB RAM and 4K Display as well as LiteON 512GB SSD, 8GB RAM and the FHD Display
You can follow the guide to install Catalina on your own machine: guide