/u/porkinstine is on the dot. People greatly exaggerate the maximum wattage you need for a power supply. I believe it comes from the days when there were a lot of dodgy power supplies and units built to the wrong ATX standard. You'd find units that said something like 600w and half of that was on the 5v line which was silly as modern power supplies use the 12v line for almost everything now. The way to overcome that back then was to buy the most powerful unit you could afford. These days we know the worth of each brand and how reliable they are. There are many lists out there to aid you.. There are also accurate power supply calculators around.

A useful piece of information is that the recommended system power on the nVidia Geforce Specifiation Sheet is for an entire high-end system. Using Ohm's law also shows that a 1080Ti uses about 20 amps at 12 volts.

I recently built a 7700k (OC'd), GTX1070, bunch of fans, SSDs and it's running off a Silverstone ST55F 550 watt. It's rock solid. Mine is a similar build.