The following forum post should help.

https://www.dell.com/community/Inspiron-Desktops/Inspiron-5680-GPU-upgrade/td-p/7252255

The base model with 460W power supply would NOT SUPPORT a 2080.

Non dell cards would require SECURE BOOT OFF and Legacy Option Roms ON.

Alienware Aurora  models List a build that includes RTX 2080 when it has 850Watt power supply.

Dell does carry the card

https://www.dell.com/en-us/work/shop/accessories/apd/aa341206

Inspiron 5680 with 460w PSU

is qualified to run these OEM video cards

XHY8P Nvidia GeForce GTX 1080, 8GB,  180w
06MKK Nvidia GeForce GTX 1070, 8GB,  150w
2FNM3 Nvidia GeForce GTX 1060, 6GB,  150w
CD6TT Nvidia GeForce GTX 1060, 3GB,  120w
24K8H Nvidia GeForce GTX 1050, 2GB,  75w
J41KN AMD Radeon RX 580, 4GB 160w
02H81 AMD Radeon RX 560, 2GB 75w

I have already upgraded the 460w psu to a 650w and the oem gtx 1060 3gb to a msi gtx 1070. Process was quite simple.

I guess what I really wanted to know is if my motherboard was compatible with rtx cards? Regardless of the size of my psu. 

The guy in this post has a 2060 so it looks fine.

https://www.dell.com/community/Inspiron-Desktops/Inspiron-5680-Gaming-upgrades-I-ve-done-over-the-past-year/td-p/7235704

FWIW on the previous posters PSU worry. I have had a GTX 1080 since the PC first came out and never changed the PSU and have never had a problem. I'm sure your 650 watt is plenty.

Stock 460W is not supporting RTX 2080.

What about a 2060 or 2060 super?

What PSU did you use and did you upgrade to RTX gpu?

If you still remember this post, what PSU did you upgrade to?  I also have a 5680 with 460 watt and am having a hard time finding a PSU to jump on and get.  Any info will be appreciated.  Name, model, etc.  Thanks