I have a Optiplex 7010MT with a new power supply. It is possible to install 2 pci-e graphics cards? The socket second socket it there but can I use that one for a second graphic card?
Yes and no. The black PCIe according to the manual is 'wired' as a 4x and not a 16x so if the machine will allow you to put in a graphics card and run it, it will only be about 25 percent useful.
I'm not exactally sure. Sometimes Dell uses custom form factors and sometimes they do not. Its also possible the mount points of the motherboard would be different even if the size of the board is 'standard'. On top of that, you may run into the pinouts on the motherboard being different then what is in the case.