Computer shuts down in some games.

I got a brand new Dell Optiplex 7040 minitower from another country. I was able to play older games with it without problems such as the 1st witcher.

I replaced the videocard with a geforce gtx 1050ti 4gb to play newer games. My PSU at this time was the one that came with the pc which is 190W. This time, I can play newer games with significantly better graphics i.e. Tales of Berseria, Breath of the Wild, World of Final Fantasy. But when I try to play other games which I think is more "graphics-intensive" like witcher 2, rise of the tomb raider, total war, my pc would shut down as soon as I get control of my character. I tried opening witcher 1 again (which was previously problem-free) but my pc now shuts down too. I figured that this might be due to the fact that my PSU isn't enough for the 1050ti GPU I installed. So, I bought a corsair 450W. However, the same thing is still happening. Is this really due to insufficient power or another thing entirely?

My specs:
CPU: Intel Core i7-6700 @3.40GHz
RAM: 8 GB
GPU: geforce gtx 1050ti 4gb
PSU: corsair 450W
OS: windows 10 64-bit

Also, I tried monitoring my computer temperature but there seems to be no problem with it. Temperature does not go more than 60 C. I also tried running GPU stress test Furmark and no problems come up.

Your help is greatly appreciated. I'm just about at the end of my wits here. Thank you!