I have used this 750 Ti with Dell optiplex 9020 MT which has PSU of 290Watts, it works fine...
TBH i have to purchase these Optiplex 7040 MT desktop PCs for a client. Where client has specified both desktop to be 7040 and graphic card to be 750ti
this is what its written on optiplex 7040's data sheet.
Standard 240W PSU Active PFC
240W typical 85% Efficient PSU (80 PLUS Bronze) ENERGY STAR complaint, Active PFC
240W typical 92% Efficient PSU (80 PLUS Platinum); ENERGY STAR complaint, Active PFC