We tried reaching you on a private message but did not receive a response. Please feel free to write back whenever you are available.

I can understand you are sending automatically private messages but posting automatically on the forum as a moderator is a total failure on your side. The private messages ask for a service tag while i have implied in my post that I have not yet purchased this laptop and my purchase depends on your answer. I hope now a human reads my posts and provides a relevant reply. 

Vag,  I hope you are okay, as sometimes people might not interpret correctly or rush to answer.  I hope you receive an answer soon,  from DELL.   You could have answered your private msg,  by correcting him/her and moved on happily. 

@Vag  PCIe x4 isn't a requirement for an eGPU.  Several users have gotten eGPUs running on systems that only had PCIe x2 interfaces wired to their TB3 ports, such as older XPS 13 and XPS 15 systems.  There's a bit of a performance penalty there of course, but PCIe connectivity isn't a huge factor on overall performance, which is why PCIe x4 works reasonably well even though in a desktop system the GPU would use a PCIe x16 interface.

As for whether the system supports charging, Thunderbolt 3 does NOT guarantee that a system supports charging via that port.  However, the TB3 port description in the Setup and Specifications document for the 7791 says, "Supports Power Delivery that enables two-way power supply between devices."  The fact that it mentions two-way power certainly makes it sound like it supports being charged from that port.  And the fact that it's designed for a 90W power source makes that even more likely, since it's certainly possible to deliver 90W over USB-C.

@MaxouXou  It supports Thunderbolt 3, so an eGPU should work.  From what I've read about eGPUs (which is admittedly not a ton), they can still be a bit finicky, but the necessary hardware is there.  And if your system has an NVIDIA GPU built in, then I'd strongly recommend using an NVIDIA GPU as your eGPU rather than an AMD GPU, since apparently using GPUs from the same vendor mean you're less likely to encounter driver issues.  And when both GPUs are NVIDIA, then the built-in NVIDIA GPU is automatically ignored when the eGPU is present.

I have the same question as Var!

So finaly, what is the answer? eGPU compatible or not?

thanks

Thank you jphughan for your advice.

Great if eGPU can run on Inspiron 7791.

But if I want to try, it's an expensive try!

eGPU cases are very expensive and having a good graphic card too!! So maybe it's more interesting to buy a regular computer for gaming and keep the 7791 for the first use I buy it for: Music DAW.

@MaxouXou  You can definitely get better performance for a given amount of money when setting up a gaming desktop rather than a gaming laptop.  As you say, the eGPU enclosure alone is somewhat expensive.  But then again, buying an entire desktop if you don't already have one isn't cheap either.