mineclj2000 :
PSU: Unsure. Somewhere between 200-300 if I am correct.
You should definitely find out exactly what kind of PSU you have. Open the side of your case (ideally with the system powered off) and it will likely be printed on the side of the PSU somewhere. If it's around 250 watts or more, that will likely be good enough for a GTX 1050 / 1050 Ti, which should draw around 70 watts while gaming. Less than that, and you probably wouldn't want to go with anything more powerful than a GT 1030, which should draw around 30 watts, similar to the power used by your existing HD 6450. The GT 1030 is a lot newer though, so it should be multiple times as fast. A 1050 is about twice as fast as a 1030 though, so if your PSU has the power to run it, it would be a better choice if you are aiming for steady frame rates in those games. And a 1050 Ti should be somewhere around 25% faster still. The 1030 tends to be decent enough for resolutions around 720p, while the 1050 and 1050 Ti are better suited for 1080p. CS:GO and Fortnite are less demanding than many games though, so you "might" be able to manage decent frame rates at 1080p with a 1030, if settings are lowered enough.
mineclj2000 :
Curious Question: Why is an AMD graphics card running with an Intel based motherboard? (Aren't they like competitors?)
Intel doesn't currently even make dedicated graphics cards (though they apparently have plans to within a couple years). Even if they did, it's perfectly normal to have components from competing companies together in a system, since graphics card and most other components are designed to be compatible with one another. A company like Dell simply selects which components they feel will go best together for a system at a given price point.