jankerson :
Roland Of Gilead :
CPU - 65w
GPU - 250w (max)
Other Hardware - 100-150w
GTX 1080Ti can pull well over 300w.
The 8400 will pull more than 65w, more like over 100w due to turbo boost.
The load for that system would work out about 450W mark. You can try it here : http://www.coolermaster.com/power-supply-calculator/
Obviously the calculator isn't exact but will be close enough. I think about 450w is about right. There may be slight spikes above that, but ballpark, it will be in that region.
Here you can see rough gaming usage for a 1080ti as tested by tom's. Sure 3rd party cards may have require more, but for the purpose of getting a ballpark, and not knowing the exact card details, as i've said it's pretty close:
https://www.tomshardware.com/reviews/nvidia-geforce-gtx-1080-ti,4972-6.html
I would agree that the 1080ti could spike close to 300w but it happens very rarely, and is card dependent.