I think there are a few models with a 6-pin power connector like GIGABYTE GeForce GTX 1050 Ti GV-N105TWF2OC-4GD .
The 6-pin is basically used in some models for overclocking and pushing the GPU to work at higher clocks/speeds (usually on 2-fan models). By default 1050 Tis need 75W to work which is provided by standard PCIE gen 2 and 3 slots.
Dell, however, sometimes implement proprietary standards in their devices.
On paper with a 500W PSU, a graphics card with a 6-pin PCIE power connector from the PSU should work. I would check with Dell support before buying. If it's a hardware electronics design which limits the board to only provide 50W adding GPU with a 6-pin PCIE power connector is a gamble. Because that board's electronics are...