Your power brick has nothing to do with an eGPU.
You'll need many things, including an actual desktop spec power supply to run it.
Have a read through this:
https
/www.reddit.com/r/eGPU/comments/5jpf2x/diy_egpu_101_introduction_to_egpu/
and this:
https
/www.reddit.com/r/eGPU/comments/5vztqs/the_egpu_resource_list/
Your primary concern is this:
" eGPUs can be connected through one of the following options: mPCIe (mini PCI Express), Expresscard, Thunderbolt1 or 2, M.2, and finally, Thunderbolt3."
Does your Dell have any of those?