Must use Dell or PNY or Gigabyte or MSI LOW PROFILE Single slot card. GT1030 is the only thing I would recommend. Anything more requires optional 365W power supply with TOWER Model. 

Vostro 3470 can be purchased with ubuntu pre installed.

https://certification.ubuntu.com/hardware/201711-25909

https://www.gigabyte.com/Graphics-Card/GV-N1030D5-2GL#kf

https://www.msi.com/Graphics-card/support/GeForce-GT-1030-2G-LP-OC

https://www.dell.com/en-us/work/shop/accessories/apd/AA362018

When installing an after-market graphics card into a Windows PC with UEFI secure boot enabled, the system may not boot.  This is true for ANY PC not just Dell.

http://nvidia.custhelp.com/app/answers/detail/a_id/3156

https://www.youtube.com/watch?v=2y32mBdZHJY

Dell A9763687

https://www.dell.com/en-us/work/shop/accessories/apd/a9763687

8CCF1 Nvidia GeForce GT 1030, 30w is for tower only or you have to make your own bracket.

PNY  VCGGT10302PB

https://www.pny.com/geforce-gt-1030

Dell A9763687

https://www.dell.com/en-us/work/shop/accessories/apd/a9763687

 Vostro 3470. 

https://topics-cdn.dell.com/pdf/vostro-3470-desktop_owners-manual4_en-us.pdf

https://topics-cdn.dell.com/pdf/vostro-3470-desktop_service-manual_en-us.pdf

DELL 3470

OPTIONAL CARD