My i5 8600k OC to 5.0GHz + RTX 2070 while gaming is 345 watts from the wall. With 80% power supply efficiency the PC is pulling 272 watts from the PSU. The GTX 1080 ti is a 250 watt card and the RTX 2070 is 185 watt card so add 65 watts and you will have 337 watts pulling from the PSU.
i5 8600K OC 5.0GHz
Motherboard Gigabyte Z370-HD3
G.SKILL Ripjaws v 16GB F4-3200C14D-16GVK XMP Speed 3200 14-14-14-34
EVGA GeForce RTX 2070 XC ULTRA GAMING
ASUS VG279Q 27" 1920x1080p 144Hz Gsync compatible