PSU For a build

Solution
yes for a Watt usage, 520W is enough.
Seasonic is a Decent brand, but people will always say why not buy this one or that one.
But spcifically, that PSU will work fine with your build.
Recommended wattage for that gpu is 380w, so the Seasonic S12-II 520w is absolutely perfect for the application. Just be aware that it is a group regulated design, and as such can have issues in ultra low power states (really deep sleep) on any Intel cpu Haswell or newer. Simple fix, in bios set C-states for C3 as lowest sleep state.
 
Do you already have that PSU?
You can usually find a much better power supply for a similar price, like the Corsair CX/CXM grey label, Cooler Master Masterwatt, Be quiet System Power 9 or Pure Power 10 400W+, Corsair vengeance.

Otherwise, it is compatible with your system besides the lack of support for C6/C7 sleep states.