650W to 750W, minimum 80 Bronze efficiency, compatible PCIe power cable connectors for your GTX 1080 - it depends on the model, 1 x 24-pin 1 x 8-pin ATX connector for the M/B.
My advice make a research of your own. And don't cheapskate about it especially if you want to O/C.
Use sites that know some stuff about PSU's and have some legit reviews like
http://www.jonnyguru.com, Aris Mpitziopoulos here at
www.tomshardware.com has some great reviews also...... and then use the pcpartpicker.com to compare the prices of your findings.
If I had to choose between the 80 us$ no matter what, I would pick the
Corsair CX650M
it has 2 x PCIe 6+2-Pin Connectors.