99.5% of the time the required PSU is determined by the GFX card.
Add up the wattage of each component and multiply by 1.25 to 1.50
Example (OC in parenthesis):
7700k = 90 watts (130 OCd)
MoBo = 30 - 40 watts
GFX Card = 75 - 350 watts
Everything else 40 watts
Say that totals 400 watts ...
1.25 x 400 = say 500 watts
1.50 x 400 = say 500 watts
If buying new , a S12 520 Seasonic would be good here and at $34 for a jonnyguru 9.7 rated PSU Id say that's a no brainer whether you get 300 - 500
https://pcpartpicker.com/product/fZyFf7/seasonic-power-supply-s12ii520bronze
http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story5&reid=185
But the XFX 450 watter will serve just fine w/ loads up to 360 watts or so