I am using 3 screens, besides the standard power supply also an external one on the usb-c. A picture would say everything but here there is no possibility.

This function does not work for me. It depends on the PC. In my case: one monitor runs over it, the second does not.

Hello, I am unfortunately not in the computer business at all. I just bought this docking station to connect my laptops to a large screen and I am very happy with it. I can only advise you to contact a specialist if you want a technical recommendation. Good day and best regards.

Mains cable and two type c to type c cables

No, this docking station requires a USB-C with video output. I wouldn't recommend it anyway, it's a piece of kit; only one HDMI port supports 4K@60Hz. https://asset.conrad.com/media10/add/160267/c1/-/gl/002249726ML00/bedienungsanleitung-2249726-renkforce-rf-4499452-usb-c-notebook-dockingstation-passend-fuer-marke-notebook-dockingstations-universal-inkl-ladef.pdf