Do there exist any products that provide USB-C to DisplayPort with USB Power Delivery?
Usb type c to display port adaptors with 4k 60Hz resolution are available on the market. 

In order to get a 4k 60Hz resolution output on the display port side your usb-c port must support Display Port alt mode. Laptops that have this type of usb-c ports are MacBook, ChromeBook Pixel™ and Dell™ XPS™ models 15 and 13.
When the usb-c port does not support the Display Port Alt mode then the max resolution is limited (mostly to 1080p) regardless of an extra power supply for the adaptor.