i5-4670 cpu can be upgraded to i7-4770, 4790, or 4790k (No overclock support in 9020 bios).  but cpu upgrade to i7-4790 brings very small fps performance boost (see next reply).  i7-4790k brings small boost. 290w stock psu can be upgraded to Optiplex XE2 MT 365w psu (oem) that has black PCIe connector (in addition to Dell proprietary 8 pin+4 pin white) D365EM-00 or HU365EM-00.  DP/N 7VK45. you can also use any reputable brand aftermarket ATX psu that has black PCIe and a 24-to-8 pin adapter.
Hey I have Dell optiplex 9020 MT with a 4670 and looking to put in it a gtx 1660 ti what psu and cpu can i get
Dell optiplex 9020 MT psu, cpu and gpu upgrade