U3225QE (and most likely U2725QE) only connect with TB3, not USB4

How can I tell if TB3, TB4 or USB4 is negotiated between monitor and computer?

@dellmaxx​ 

There is no TB4 connection. There only is TB3 or USB4. TB4 basically switched the underlying connection from TB3 to USB4. And they add a few minimum requirements on top (because USB4 covers quite a bit of range. TB4 is basically USB4 with slightly raised minimums).

For the differences between TB3 and USB4 connections:

TB3 only knew PCIe and DP tunnels (and technically host-to-host or "TB Networking").

USB4 added USB3 tunnels as well. So you can always look at on which controller USB3 and USB2 devices appear. With TB3, each TB3 controller connects via the PCIe topology and comes with their own PCIe USB3 controller which handles all USB2 & USB3 devices attached to that controller. With USB4, this is not the case, as USB2 devices connect via a USB2 hub(s) back to the host and USB3 devices through the new USB3 tunnel (and hubs).

So from Device Manager in View by connection, you can easily tell, if the TB/USB4 controllers on the PCIe bus have USB3 controllers or if there are just a bunch more USB3 hubs behind your hosts USB3 controller (and you cannot really tell from Device Manager that those USB3 connections are partially routed virtually through those USB3 tunnels inside USB4 connections).

Actually, USB2 and USB3 devices behind USB4 are likely to connect to different controllers.

Tools like USBTreeView can also visualize the USB topology, controller and devices.

And here an example of what Windows' USB4 drivers can draw of USB4/TB3 via the Device Portal:

This shows Host -> Caldigit Element Hub (TB4 Hub) -> U3225QE -> U3225QE

And you can see the DP, PCIe and USB3 tunnels in the USB4 connection to the TB4 hub. But then only DP and PCIe tunnels (TB3 connection) to the monitors.

And you can also see that all of them (TB4 hub and monitors) use the same TB4 controller that just does not work right.

And because of that, a USB4-only device (without TB3 backwards compatibility that Intel controllers include), will not appear here when chained to the last monitor, because there is no USB4 available there. While, if they were connecting with USB4, it would have appeared as a 4th device in the chain (but also without DP tunnel, as the host only has 2 available and they have already been used for the 2 monitors).

Re:  How can I tell if TB3, TB4 or USB4 is negotiated between monitor and computer?

If you have the same monitor as OP, connecting it to a Dell laptop which has thunderbolt 4 and with the laptop power adapter disconnected.

Boot the laptop and accessing its BIOS settings.  At the battery status and charging status, verify if the power input is 140w, that means your monitor and laptop was negotiated at thunderbolt 4.  If the power input is 100w, that was indication for thunderbolt 3 or USB 4.

@Chino de Oro​ 

This is completely wrong. USB-PD power negotiation is completely independent of USB4/TB3.

Any device can support EPR to read the monitors 140w supply, even TB3 devices (they most likely won't, but a new TB3 device could). If they don't, the will see the max SPR wattage (which Dell coincidentally claims is 90w, in violation of the USB-PD specs' power rules).

TB4 launched when EPR did not yet exist. So those older devices will definitely not know of EPR. In fact, most TB4 cables do not support EPR and will block the power supply from even offering more than 100w.

And basically no laptop that needs only 100w at 20v will support EPR in the first place. Dell even had problems leaving those 20v behind, to the point where they also have violated the USB-C spec and are using more than 5A, to still stay at the 20v they are used to, rather than increasing the voltage the Notebooks run off of to 28v or even higher.

Sorry @Ray519 , although posting in your thread, my post was responding to @dellmaxx question.  While I don't talk like a geek or sound like a know-it-all, I put my little advance computer knowledge to practical use and helping out other users in this community at my free times.

Some of users did not respond back the result but many have confirmed that, with my help, their computer problems, issues were resolved.  Not sure of what purpose and time your skill set have achieve in here.

In all scenario below, the Displays Team could achieve USB4 speeds. Testing configurations =

XPS 13 Plus 9320 TB4 --> U3225QE TB4 cable --> First U3225QE #7 TB4 upstream port
First U3225QE #5 DP out port --> U3225QE DP cable --> Second U3225QE #4 DP in port

XPS 13 Plus 9320 TB4 --> U3225QE TB4 cable --> First U3225QE #7 TB4 upstream port
First U3225QE #6 TB4 downstream port --> U3225QE TB4 cable --> Second U3225QE #7 TB4 upstream port

Latitude 7450 TB4 --> U3225QE TB4 cable --> First U3225QE #7 TB4 upstream port
First U3225QE #5 DP out port --> U3225QE DP cable --> Second U3225QE #4 DP in port

Latitude 7450 TB4 --> U3225QE TB4 cable --> First U3225QE #7 TB4 upstream port
First U3225QE #6 TB4 downstream port --> U3225QE TB4 cable --> Second U3225QE #7 TB4 upstream port

They also connected an OWC TB4 dock to both models above. Then connected both U3225QE to separate OWC TB4 dock TB4 ports. Dell does not test dual monitor MST daisy chain from any dock.

@DELL-Chris M​ That is a cool answer.

I note: Dell has not tested an AMD USB4 controller. And sadly, I only have the one model of AMD notebook at hand, so cannot really conclude whether it not connecting at all (directly via TB4 port) is an AMD problem or sth. specific to my 3rd party notebook model.

But for the speed, I am getting a 40G connection and the display output works as intended. Notably, the speed for both TB3 and USB4 is quoted as "40G" and Windows does not show a difference between both in the USB4 UI.

The difference is only visible in the PCIe topology. Because via USB4, the USB devices attached to the monitors would be attached via USB3/2 back to the host. And via TB3 all those USB devices are attached to PCIe-USB3 controllers in the monitors and any USB4-only device (not TB3 backward compatible) will cease to function on the TB-outs of the monitors (which is against TB4 specification of total USB4 compatibility).

The connection type in and of itself not a problem, as it does not really break sth. for the monitors. I just suspect that my AMD notebook has a problem with a USB4 controller refusing to make a USB4 connection and instead only making TB3 connections. And that that causes the main problem for me. Because both the notebook and the monitors behave unusually.

And then, the fact, that a TB4 monitor seemingly unable to make USB4 connections with 2 TB4 certified devices seems to indicate some type of problem, that will likely affect other customers in rare and hard to find ways, because nobody will expect it and most people would not notice the difference (in connection) and only notice when sth. else does not behave as expected from TB4.

Here no difference is visible and it works. Even behind a Dell TB3 dock (actually, only putting that dock in-between makes the monitors recognized on the AMD notebook's TB4 port).

 But the USB3 devices are all behind PCIe connections, which only happens for TB3 connections.

Whereas, with actual USB4 connections, they would be under those native USB3 controllers here instead: