Power supplies are not a single rail and a single spec of WATTS Besides not physically fitting in the case the unit has insufficient power on the 3.3v/5v combined rails.   Power supply that would work must be OUTSIDE the case. EVGA 700BR [URL] [IMAGE]150W combined on 3.3v/5v rails              
I have a GTX 1650 EX and a Silverstone ST40F-ES230 for my 990, I realized both components are to big for the original case, So I have a custom case big enough for both components. (Built it myself) I have all the parts in except the Silverstone ST40F-ES230 (the original PSU is with the other components) and the 1650, I'm just wondering if the power supply has all the connectors for a Dell Optiplex 990 DT motherboard   I can sell the Silverstone ST40F-ES230 for a 400 watt compatible power supply.
Can a Dell Optiplex 990 DT use a Silverstone ST40F-ES230 power supply in a 
custom case