I have a MSI 760GM-P34 (FX) mobo, I'm needing to upgrade the power supply on it as I'm also upgrading the GPU as well, it currently has a R9 250, I'm planning on buying a gtx 960 and need a power supply big enough to run it, any help? I know my mobo is a 24 pin atx but I'm not confident enough to make the purchase on my own. Anything around 100$ would be fine, thanks for the help.