petecharles1 :
Is a Seasonic Sii 520w 80+ Bronze a good PSU to run an i7 6700k and a GTX 1080?
https://www.newegg.com/Product/Product.aspx?Item=N82E16817151094
It does have enough power. Does it have the cables necessary for the 1080 you have or are looking at? Idk. I also have the sneaking suspicion you will be overclocking the CPU and GPU meaning you need something with a wee bit more power. Technically speaking my answer is yes IF it has the necessary PCIe supplementary power cables. Best solution with OC'ing in mind? Not imo.
Nothing less than
https://www.newegg.com/Product/Product.aspx?Item=N82E16817438053 with OC'ing in mind.
I suspect the system will draw a little under 400W at load. I think you will be fine with the Seasonic. If I had those parts I'd want to have a much more efficient PSU. I think The G2's warranty might last longer which does add value.