Quality matters more than strictly wattage. A quality 700W PSU would be more than capable for an R7 1700 + 1080TI
A junk "700W" PSU may only be capable as a paperweight.
Which PSU are we talking about specifically?
You're talking a 65W TDP CPU, a 250W GPU..... so comfortably under 400W max load, before overclocking.
A bit of a 'buffer' would be good, for both overclocking and for peak efficiency.... so a quality 600W minimum PSU would likely be a smart choice..... but the actual model/internals matter more than the wattage.