I'm going to assume that your power supply is a 230W from an OEM, so I'm going to suggest to you to upgrade your power supply first. And given the fact that your CPU is power hungry, you'll struggle to power even a GTX 750/1050.
I may be wrong with the wattage of your power supply however, if it's a 300W, then you can power a GTX 1050.
Core 2 Quad Q6600 will work really fine with GTX 1050 Ti!
But before adding a 1050 Ti, add another 4GB DDR2 RAM for a total of 8GB if possible or you can add another stick of 2GB DDR2 for a total of 6GB which is enough for most Triple A titles
And I would recommend to upgrade your power supply to a better one, I guess you live in India so this will be best - (https://mdcomputers.in/antec-450-watt-bp450s.html)
Or If you are from any other country where Amazon.com can deliver directly then search for the best 450w psu for 20$ to 30$
I think the current pricing of GTX 1050 Ti is very high, Try to buy it second hand for bang for your buck!
This is all you need to take out all the juice of your PC!
Hope it helped!
A built out Optiplex 745MT would have a QX6800 SLACP,D9729 heatsink, 8GB DDR2 800 RAM, and a Zotac GTX1050Ti Mini.
It can be overclocked with Throttlestop 6.00 to 3.45Ghz
The 305W PSU will be OK for everything except the overclock.