I have a Dell Optiplex 9020 Minitower and I was planning to upgrade it by buying a new video card. I was eyeing the ZOTAC GAMING GeForce RTX 2060 Twin Fan. The only problem is i don't know if it will fit? Can it fit?
Note: The PSU is already upgraded so that is not a problem anymore.
450W should be good enough, but it has to be reliable PSU. Post the exact model on the forum to check on that. I'm not a PSU expert, won't help You with this. It's very often, that pre-built setups come with crappy PSUs.
Honestly - no idea. RTX 2060 works in about 70C. It is not that much, but if Your rig is small, with no air flow, You can experience some problems with heat inside (dunno which version of the case You have). The absolute minimum for gaming rigs should be 2 case fans (1 front for air intake, and 1 back for the output)
Check what fans You have and if You can - install some to ensure some air flow.
About the size - try to post a picture of Your rig. The best would be with unmounted cover / side wall (put link to the picture here)