GPU would work in the motherboard, but your CPU is most likely too weak for latest demanding games. It still might be a good upgrade, if you know which games you want to play and made research if said games run well on such configuration. Regarding the choice of GPU- now might be a good time to upgrade to used graphic card, like GTX950, GTX960, R7 270, R7 370 or the same GT750Ti. If buying new- RX460 is much faster than 750Ti and often costs the same.
Now, regarding the PSU- it is all about quality, so we would need to know the exact model to know if it is good enough. It is also likely it is as old as the motherboard, and parts in PSUs age.