the bottleneck can be sometimes small so you could get for example, 100fps on a game but you could get 130 fps with a faster cpu
being a old cpu, a cpu upgrade is not viable, you would need to change, mainboard, cpu and probably ram too so not a economic option
if the psu has 500w it shoul be fine, especially if you get a 1050 ti withouth the 6 pin power cable i mentioned previously
most 1050ti will ask for a 300 to 400 w psu so that was the biggest concern here and is covered