I upgraded from a Radeon HD 7770 to a 960 specifically for Fallout 4 and ended up having to get a new power supply with it, for my old one wasn't enough for the 960. I also had trouble fitting it in the case so I also needed to move a bunch of stuff in my computer aside for the beast to have enough room.
What was your old power supply? Mine is 460w. The 960 I bought needs at least 400w and a 6 pin connector and I had both.
It's a huge upgrade the fans are bigger than the old card itself. lol.
Best Buy was selling a 960 2gb for 219.
Newegg was selling this 960
4gb for 194.
It was a no brainer.