Summary

Stylish two-to-six power socket extension. Feel free to adapt it to your requirements. It is GIRA Standard 55 compatible, which is pretty common in Germany. The base is universal, you can adapt the cover to fit other models of sockets. You should use dry wall boxes Ø68mm and 35mm deep to make the installation compliant.
I printed it in PETG with tree support as per printing recommendation pictures. For better stability I put the 3 covers in a triangle formation and connected these with very thin rectangles, which I just cut off after printing.
FreeCAD project file is attached.