I am creating this thread with the hope that others who have gone down the eGPU path with their Mac Minis can also share their experiences. I did a great deal of research on the internet trying to minimize the risk of wasted money and time, but it was still difficult to eliminate the uncertainty completely. Hopefully, someone will find this particular setup and experience helpful. Short Background I replaced my 2017 iMac with the 2018 Mini hoping to improve my productivity. For the most part it worked well, with the exception of the lackluster integrated GPU. As the Mini was the only option in the product line that met my needs, I purchased an eGPU. Hardware 2018 Mac Mini, 6-core i7, 32GB RAM, 512GB SSD, 10 Gigabit Ethernet. Link:Sapphire Vega 56 Pulse. Link:Sonnet eGFX Breakaway Box 350W. Link:6-pin PCIe power connector to 8-pin PCIe power connector adapter. Link:Samsung X5 external SSD with the intent of installing Windows on it, but had some concerns (explained later). Link:LG 43UD70-B 4K display connected to eGPU via DisplayPort. Link:ASUS ZenScreen MB16AC portable display connected to Mac Mini (iGPU) via USB 3.1 (also powered by it). I have a dual monitor setup with a little portable one to the side (photo below). I think having 2 screens will make this easier. The 1st screen is connected to the eGPU and the 2nd screen is connected to the Mac Mini (iGPU). Notes I actually had my heart set on the Razer Core X because it seemed like the best bang for the money. However, I could not find it anywhere in stock. I needed an eGPU as quickly as possible for work, so I purchased the cheapest Sonnet 350w version thinking that it would be plenty for the Vega 56. On Sonnet's compatibility page, they state that the 350W version does not support the Vega 56 and steer customers toward the more expensive 550W version. This is odd because Sonnet lists that the 350W version can support up to 300W GPU, and the Vega 56 is rated at below 200W. The Vega 56 requires 2x 8-pin PCIe power connectors. The Sonnet 350W comes with 2x PCIe power connectors as described below: One 6+2 pin PCIe connector. One 6 pin PCIe connector. I plugged the 6+2 pin PCIe connector into one of the 8-pin slots on the Vega 56, and purchased a 6-pin-to-8-pin adapter on Amazon for $7. I am not sure if the adapter is even necessary, but I wanted to be safe and it seems to work. Interestingly, for use with the Mac Mini, I find the 350W more upgradeable than the 550W version, because the 550W version reserves more watts (85W vs 15W) for power delivery for charging laptops and such, siphoning those watts away from potentially powering the GPU. I have no need for it because I will not be charging anything with it and would be happier if everything went to the GPU. Finally, I have been running with the eGPU with the cover off of the Sonnet enclosure to make sure everything is working before closing it up, and I was surprised that the fans on the GPU were not spinning at all. It seems that they only spin up at some threshold temperature. All this time, I was under the impression that the fans were spinning at all times, slower or faster depending on the temperature, but always. But this is not the case. All this makes for an extremely quiet setup. The enclosure itself is very quiet, too, so I cannot even tell if it is on. I am happy with the final outcome. The frame rates are great, and Xcode seems to take full advantage of the GPU. I am even happier because the Sonnet 350W was only $200 as opposed to the Razer Core X's $300 and Sonnet 550W's $280 price tag. If needed, the PSU can also be upgraded. I upgraded the PSU. See post #20. Glossary: "error 12" This is where most people get stuck on. The "error 12" message is displayed in device manager (in Windows) for the GPU and it means "This device cannot find enough free resources that it can use." It has to do with the addressing space available to an eGPU, and an eGPU needs a lot of it compared to other devices. To work around it, you can disable other PCIe resources in device manager to free them up. This seems to be more of an issue with Macs that have both an integrated and a dedicated GPU, so I thought it shouldn't be much of an issue for us. I ran into it, though. So it's good to know what it is. Whenever you see "error 12", this is what it means. Installation: MacOS Plug-and-Play. It should just work. None of the cables I tried initially worked. Make sure you are certain that your cables will work or expect to waste a lot of time. Installation: Windows Windows 10 was problematic. It was a windy road to get it to work. Prerequisites: The first thing you should do is to install Windows (I installed the 1803 April update, though others also had success with 1809) via Bootcamp. I know that many people want to install Windows on an external SSD, but I would suggest creating a partition on the internal SSD. I purchased the Samsung X5 because I planned on installing Windows on it, but I decided against it because of the possibility for an "error 12" (not enough resources described above) issue. If this happens, then there was a chance that I would have had to disable one of the Thunderbolt 3 controllers. I wanted to eliminate as many complications as possible. Make sure you can boot into Windows without the eGPU and download the GPU driver. Steps: Disconnect the eGPU from the Mac Mini. Connect the ASUS portable display to the Mac Mini. Reboot and press-and-hold the "alt" key to display the boot options (I found my bluetooth Apple keyboard unreliable, so I used another USB Keyboard). Boot into Windows. Connect eGPU to the Mac Mini. The main monitor should also be connected to the eGPU. Use the Thunderbolt 3 port closest to the HDMI port. Install the GPU driver. At this point, I saw the "error 12" in device manager for my GPU. So I disabled "PCIe Root Port #2 - A339" in device manager, then rebooted back into Windows. This time, my main LG 4K monitor that was connected to the eGPU was showing the login screen, meaning that the eGPU was detected. Except, none of my keyboards were working! All I could do was to force a shutdown by holding onto the power button on the Mac Mini. I disconnected the eGPU from the Mac Mini and booted back into Windows. I re-enabled "PCIe Root Port #2 - A339" in device manager. I shut down Windows. I reconnected the eGPU to the Mac Mini and booted back into Windows. I was planning on disabling the PCIe controller for the 10 Gigabit Ethernet in case of the "error 12" issue, but... Everything was magically working. The main monitor was showing the login screen and my keyboard was functional. I was afraid this was a fluke. I tried booting from MacOS to Windows and from Windows to MacOS many times, expecting something to go awry. However, it is working every single time. I read a post from someone where he said that booting to Windows fails if the eGPU is connected, but I do not have this issue. I also read that the poster had to disconnect the NVMe SSD before booting to Windows, but I do not have this issue either. I was also afraid that I would have to disable the 2nd Thunderbolt controller, which means I would not be able to use my Samsung X5. However, this also was not the case. For some odd reason, everything just works. Benchmarks Division 2 in Windows in 1440p, I am getting anywhere from 45+ to 60 FPS. Monster Hunter World in 1440p, all over the place from 30 - 60 FPS. Rise of the Tomb Raider in 1440p, 60 FPS. Grand Theft Auto V in 4K, 60 FPS. I ran it twice. One time in 4K in medium quality (first image). The second time I ran it in 2K in ultra quality (second image). Unrelated to this, but I just have to brag. The Samsung X5 is truly amazing. I know the T5 is fast, but having experienced the X5, I am spoiled. I was able to copy 43GB of random files (of varying sizes -- tens of thousands of files) in less than a minute. Edit 2019.4.12 Should work with Windows 10 update 1809 as reported by @F-Train. See post #12 if you're trying this with a single monitor. Edit 2019.4.14 Simplified the steps.