I didn't find another Dell Community thread for the 380 + Xeon, but I found one for the 745 which wasn't that much different from the 380.

https://www.dell.com/community/Optiplex-Desktops/745-CPU-upgrade-to-Xeon/m-p/6056641#M23964 

Hi @mesinik,

I just noticed your post in the unanswered list.

Modded Xeon's were never tested nor supported by Dell for the 380.

If you really want a Xeon and ECC RAM, a Dell Precision is a good place to start.  Some refurb Precision's are priced as low as Optiplex's.

I don't know if you know - Many Xeon's don't have internal graphics.  In which case, refurb Precision's typically come with a GPU card..

By the time money is spent on a Xeon and ECC RAM, you might as well get a Precision.  380's can't take ECC RAM that I ever heard of.  Expansion options are limited with the 380, even compared to Optiplex's newer than the 380 with higher model #'s.

Just an example of some Dell Precision's.  You're more than welcome to expand your search - Amazon, newegg, other model #'s, and so on.  https://www.ebay.com/sch/i.html?_nkw=dell+precision+t1650&LH_ItemCondition=2500 

I had optiplex 380 with xeon e5450 running in stock cooler and speed.

runs great in windows 10 with radeon hd 6450.

But my rams are reguler not ecc one.