The 360W PSU might not be big enough. NVidia says 400W minimum. And have you read this thread?  I don't see a Legacy option in BIOS listed in the XPS 8940 Service Manual, so even with Secure Boot disabled, this card may be a no-go...
I'm getting the 3 amber 2 white flashing on power button, which in the manual is PCI, video card/chip failure.... This GTX 650 TI works without issue in other PC's. I have turned off Secure Boot. Re-seated card a couple times. Still have the flashing error code. Is there something I'm missing? I know its an older card but it's fine for what I do. I have downloaded the latest Nvidia drivers. Have the newest BIOS... I just don't want to burn the house down or fry a new computer lol. I have the 360 watt option with 6 pin which should be enough, all I have is i3 10100, 16GB RAM and one hard drive....    
XPS 8940, Flashing error code with GTX 650 TI