GTX 980ti is a very power hungry card.
Back when i was using one i was using a 4770K on a Z87 platform with a 550W XFX XTR 80+ Gold PSU (a very good unit) but when i was playing battlefield online for more than 10 or 15 minutes the fan on the powersupply would go nuts...it would ramp up to max speed for like 15 or 20 seconds and then it would come back down...for a minute or so, and then rinse and repeat...
So yeah, the PC wasn't turning off or anything, but the PSU was suffering, and it was as good as it gets for a 550W unit. SO...others aren't wrong when they recommend some 550W PSU, but if you overclock the card a bit, and use an unlocked CPU, be prepared for that kind of stuff...
My advice is: PSU is a thing that IS future proof...so it's worth spending a bit more to get a unit that will last you for your next few builds with room to spare...
i ended up having to sell the 550W PSU and i replaced it with a EVGA G2 750W gold and now the thing is dead quiet and reliable.
I would recommend a 650W Gold rated PSU or better, that has good reviews.