Yes, the RM650i is a great-quality PSU and is certainly more than enough for a rig built around an i7-8700K + 1080Ti with enough headroom for efficiency and OC.
GTX 1080 Ti @ ~250W TDP
i7-8700K @ ~95W TDP
Other basic components (SSD, HDD, Fans, RAM, MB, LEDs) @ less than 100W
TOTAL ESTIMATED DRAW = Less than 450W
Thanks for the answer, any information about 8700k's cooling needs? do you know if Cryorig H5 be enough?