planning to get a R9 390 or gtx 970 upgrade

now only have fsp hexa 500w, can i know whats the min watt psu for r9 390 or gtx 970?

i dont need to spend that much if i get the gtx 970 right?

Asus P8Z77-M
4gb Corsair Value Ram x2
FSP HEXA 500w
HD6870
i7 3770k oc 4.3ghz
aocg2460pqu 1080p