The XPS 8940 motherboard doesn't use 24 pin for power, only the 6 pin.  You can get a 24 pin to 6 pin adapter to connect your Antec PSU to the motherboard. Preferably, many users opted for an OEM 500w PSU.  These are the OEM power supply that will work with your system, Dell part number Y7R0X 500W (made by Chicony), 99TPH 500W (made by Liteon), and 5K7J8 500W (made by Delta).
Hello, My video card went out and I bought an RX  6700XT. The out of the box PSU with the XPS 8940 doesn't seem to have the power required to use this video card. I have an Antec Neo Eco 600w sitting around I thought I would use to replace the one in my XPS 8940.   I noticed however, that the Dell motherboard requires 2 4-pin and 1 6-pin connector to power it. The power supply does have 2 4 pin and if I add an adapter it will give me the 6 pin. Will this work? Also, since there is not a spot for the 24 pin connector off the PSU I just leave that off right?   I understand the case will likely not close but I am ok with that even if the power supply has to sit outside the machine. Hoping someone else has possibly done this or can comment if this will work.   Thanks. [IMAGE]
XPS 8940, upgrade to Antec Neo Eco 600w PSU