I highly recommend the AMD line of graphics cards - in my experience they have been doing much better than the nVidia cards recently. I use a R7 250 which is techically an upgrade to your card, but if you can afford the jump I would recommend pretty much any R9 instead or else a R7 260+.
Also, the power supply depends on whether you are worried about your energy bill. If you are, a 500-600 watt in the 80+ types. If not, 700-800 will allow you the most flexibility with graphics cards - some are power hogs.