Video cards usually indicate how many watts your system will need overall.
I check 1 of 3 (or all 3) places, either the Newegg Details tab of the card, the AMD/Nvidia website, or guru3d.com.
Originally Posted by AMD
500 Watt or greater power supply with two 75W 6-pin PCI Express® power connectors recommended
So a 550W power supply should work just fine for your build.
On a side note, have you taken a look at the AMD FX-4100
Its cheaper than the 970 with the power of a 980 from what I've seen, and will work with your build without any changes.
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Nobody wants to read a wall of text, formatting is your friend.
i5 3570k | 8GB G.Skill 1600MHz | R9 290 | SeaSonic 750X