RX 590 is 175W GPU, add the rest of the system at about 200W to it and you're looking 375W. CPU/GPU OC adds another 100W or so watts to it, making the max power consumption around 475W. Here, 550W PSU would be minimum but i'd go with 650W PSU since it would be more than enough for your PC (including future upgrades).
That being said, i suggest getting any Seasonic unit, in 600W range. E.g: Focus 650 (80+ Gold), Focus+ 650 (80+ Gold), PRIME SnowSilent 650 (80+ Platinum) or PRIME Ultra 650 (80+ Titanium),
Focus: 7 years
Focus+: 10 years
PRIME: 12 years (includes all PRIME models: regular, Fanless, AirTouch, SnowSilent, Ultra)
All my 3 PCs: Skylake, Haswell and AMD are also powered by Seasonic. Full specs with pics in my sig.
Min 650W Gold Certified and if intent on Overclocking and future expansion then 750-850W gold or silver would be ideal. Seasonic, EVGA, Antec are excellent with full modular connections. It's worth the extra for the best.