Vrftjkry

Just looking for confirmation here but do devices like this have their own graphics card built-in? I know it says "External video card" in the description but on many listings for devices like that, it's a bit vague.

https://www.scan.co.uk/products/startech-usb-30-to-hdmi-external-video-card-multi-monitor-adapter-with-1-usb-pass-through-port-1920x

So if a (2nd) external monitor was plugged in via one of these devices, graphics performance would probably be a lot less than the on-board graphics card on a laptop?

We've used several devices like this to add 2nd screens to laptops but they are only used by office type users. We've got a graphic designer joining and the requirements have stepped up. Getting detailed information on display ports is often tricky. For example, this AMD based laptop appears to be able to drive up to four monitors using a USB-C to DisplayPort adapter:

https://psref.lenovo.com/syspool/Sys/PDF/ThinkPad/ThinkPad%20A485/ThinkPad_A485_Platform_Specifications.pdf

I assume this method would use the on-board graphics card to drive the monitors?

But this model can't support USB-C to DisplayPort and therefore can't natively support multiple monitors?

https://psref.lenovo.com/syspool/Sys/PDF/ThinkPad/ThinkPad%20E580/ThinkPad_E580_specs.pdf

My take on this is USB-C to DisplayPort is more of a splitter kind of technology whereas the USB3-HMDI is a separate graphics chip?

It varies. The USB-C connector can directly carry various different protocols as "Alternate modes" – the port can switch from traditional USB to HDMI, DisplayPort, Thunderbolt, analog audio (on phones), possibly Ethernet.

Simple USB-C adapters use the HDMI or DisplayPort alternate modes, so they attach to the existing GPU and directly receive the apropriate signal from it (or possibly converting HDMI↔DP). They aren't "splitters" though – they only expose outputs that the GPU already provides, like traditional DP/HDMI-out ports do.

Thunderbolt-based adapters contain their own GPU (as it is just PCI-Express behind the scenes). This does not necessarily mean lower performance; on the contrary, many such "external GPU" products exist to improve performance over the laptop's integrated low-power unit. External GPU devices are noticeably larger than plain HDMI/DP adapters.

(There also exist USB display adapters based on proprietary mechanisms like DisplayLink – these show up as a virtual GPU, but the hardware is just a simple frame buffer and all rendering is CPU-based.)

But this model can't support USB-C to DisplayPort and therefore can't natively support multiple monitors?

The spec sheet shows a traditional HDMI output, and says that "two independent displays" are supported. I think this means the internal panel + one external HDMI display.

The Lenovo website for E580 claims that the model supports DisplayPort over its USB-C port, but some online reviews say that it didn't work.

My take on this is USB-C to DisplayPort is more of a splitter kind of technology whereas the USB3-HMDI is a separate graphics chip?

In both cases it's most likely that the adapter just uses the corresponding "alternate mode" of the USB-C port. Whether it's HDMI or DP doesn't change things much.

So if a (2nd) external monitor was plugged in via one of these devices, graphics performance would probably be a lot less than the on-board graphics card on a laptop?

Well, i own an adapter like this one, USB 3.0 to VGA, from another vendor... works fine for low end stuff like, in my case, programming, SSH...

BUT, for Youtube, for example, just lost frames in fast scenes. So, depends what you doing.