Will a rtx 3080 fit in my Dell 0PXWHK (Inspiron 5680)

There was a handful of users with Inspiron 5680 and RTX 3080 ran their systems on benchmark site

https://www.userbenchmark.com/PCBuilder?searchTerm=inspiron%205680%20rtx%203080

It suggested that the RTX 3080 was validated by users to run in Inspiron 5680.  However, there is lacking of information how these RTX cards were installed and which power supplies were used.

Due to variant of RTX 3080 made by different manufacturers, you should check the dimension of the selected card and compare for yourself.  For example, Dell OEM RTX 3080 fitments and power requirement can be found here  https://www.techpowerup.com/gpu-specs/alienware-rtx-3080-oem.b8258

Once you verified the fitments, you must check the power requirement to make sure that your power supply could provide enough graphics power.  For example, the Dell OEM RTX 3080 card would require x2 of 8-pin connectors.

Chino gave a very thorough answer.

Verified OP has 5680 mobo

5680 spec shows stock psu is 460w.  Power wise for RTX 3080 a psu upgrade to 650w is obligatory as already mentioned.

the 460w has a 6 pin and 6+2 pin.

psu need estimate for 3080:

Load Wattage: 566 W
Recommended PSU Wattage: 616 W

physical fit info can be gauged from user benchmark.  each user uploaded the 3080 vbios info.  but you can use the spec for a quick estimate 

spec: full length max 10.5” single or double slit width.

https://dl.dell.com/topicspdf/inspiron-5680-gaming-desktop_specifications_en-us.pdf