We're getting off track here. The OP is asking for a power supply for a 970, not whether or not an R9-390 is better than a 970. A 970 is a fine card if that is what the OP wants. If you're looking for a power supply a 650W is more than enough for a single card. If you want to run a second card later on, you're probably looking at a 750W - 850W power supply.
If you don't want to add a second card this will be what you're looking at:
https://www.theitdepot.com/details-Seasonic+620W+Power+Supply+(S12II-620)_C14P7878.html
If you want to add a second card you're looking at something like this: https://www.theitdepot.com/details-Seasonic+750W+Modular+Power+Supply+(SS-750KM+III)_C14P17189.html