Question Is 550w good enough?

That PSU is very good quality by the way, but I suggest you grab a slightly higher wattage unit if you want to use GTX 1080 Ti. You will get some extra headroom as well, just in case you want to upgrade in future, and also plan to OC the GPU.

NVIDIA recommends a min 600 Watts PSU for the 1080 Ti. That seasonic Foucs Gold might also do the job, but if you can grab a slightly higher wattage unit, then you don't have to worry much about the power draw.