[NAME] An  The XPS 15 9550 has the same issue with USB-C video output that was found with the XPS 13 9350 that resulted in this Dell KB article.  Unfortunately the fact that the XPS 15 9550 was affected didn't become clear until later, and Dell never went back and updated that KB article.  I realize that you're dealing with a Samsung display rather than a Dell display, but the forum threads here that resulted in that KB article being created also found that some third-party USB-C displays and docks trigger this issue.  I myself found that the XPS 13 9350 won't output video through Lenovo's ThinkPad USB-C Dock Gen 2, even though it works fine with a Lenovo ThinkVision M14 USB-C portable display.  Dell's KB article of course isn't going to list every possible third party product that doesn't work, but I suspect that your Samsung display might trigger this problem.  In that case, there wouldn't be a way to fix this, because Dell never provided a fix for this, or even a clear explanation of what causes the problem.  But if HDMI works, then I wouldn't worry about it.  If you wanted to use USB-C to USB-C in order to use your display as a power source, that isn't a great idea with that system anyway because the XPS 15 9550 is designed for a 130W power source, and third party displays won't provide that much power because that exceeds the USB PD 100W spec.  Dell did something proprietary on some of their systems and docks to run 130W, but that won't be implemented on third party products.  So even if you got USB-C working, your system would draw less power than it needed for optimal performance and therefore would reduce battery charging speed and possibly performance to compensate.
I connect Dell XPS 9550 to monitor Samsung LS27A600UUEXXV 27 ((2K/IPS/75Hz/5ms/Free Sync/USB C)) by cable  USB- C to USB-C (attach with monitor) but it don't work. Connect with HDMI cable is OK. So how to solve this problem. Thanks for support  
Connect to monitor