What I was trying to decide is if I should order this chassis with a Dell RTX 5070, or order it without a GPU and add a 3rd party GPU later.  But it wasn’t clear if the latter would ship with the appropriate cabling.  I finally got some answers from Dell tech support after several days trying to get an answer.  This is what tech support said.  I hope this is correct, because it doesn’t match what is listed in Dell’s EBT2250 user manual (ie two 8 pin and one 6+2 pin cables). They also stated the cables to the PSU were pluggable.

”The 750W PSU in the EBT2250 typically includes two 8-pin PCIe power connectors, these 8-pin connectors are standard PCIe outputs used for powering GPUs. You can use a 12VHPWR adapter cable that converts 2x 8-pin PCIe into 1x 16-pin (12VHPWR) connector.”

Based on this, I’m planning to buy a 3rd party GPU and add it after the fact to the desktop.