I currently use a Dell Optiplex 9020 and I have been looking to upgrade it with a graphics since my PC plays on intergrated graphics. I also do not know any power supply that can fit inside the case. the current PSU is a 255W 80+ Bronze, and I am sure that a graphics card like a GTX 970, 1060 and a 1070 (My preference) won't work with a 255W PSU.
https://imgur.com/FnktLZb
That is the PC I use
https://imgur.com/FnktLZb
That is the PC I use