U3419W, Advice needed for shorter cable specifications

@LMD75  This is strange.  The specs of the U3419W indicate that it can supply up to 90W and support USB 3.1 Gen 2 (10 Gbps).  If you only use a cable rated for up to 60W and USB 3.1 Gen 1, then that's all you'd get because those cables wouldn't have E-Marker chips to advertise that they support more than that -- but if you were ok with those limitations, then before reading your test findings I'd have said that any USB-C cable that can support 60W, DisplayPort Alt Mode, and USB 3.1 Gen 1 would be fine to use.  It's especially strange to me that the Lenovo X1C7s are behaving differently from the X1C6 systems.

But if you want a USB-C cable that's 1m, supports 3.1 Gen 2, and up to 100W, Cable Matters makes a cable like that here.  I can't speak to compatibility with your specific hardware, but I've always had a solid experience with their stuff.

As for your question about a "Dell 20GHz, Gen 2, 1m/3.2ft, DP Alt Mode USB Type-C to C cable", I don't see a link to that anywhere if you meant to include one, and I'm not sure why GHz is being mentioned here.  There are Thunderbolt 3 cables rated for 20 Gb rather than the full 40 Gb, but that's not GHz, and USB 3.1 Gen 2 is 10 Gb -- still not GHz.

@jphughan Thanks again for your input.  I also have the usual sleep /wake issues with the MacBook but that's a completely different story.

Its good to know that 1m USB-C 3.1 Gen1 60W cables are meant to work.

I think the 100W cables will all work fine and thanks for the other cable recommendation.

@LMD75  by the way, this is one more option for a 1m, 100W, DP Alt Mode cable.  It's a bit more subtle than the Cable Matters cable because of the darker marking on the cable connectors.  I actually own this cable and it's worked fine for what I've done with it, but again I haven't tried your specific use case.  This cable only mentions 4K video rather than 8K like the Cable Matters cable, but I don't know if that's because the Cable Matters cable is actually different in its ability to support DisplayPort 1.4 over USB-C or if this Anker cable would also run that and Anker just hasn't updated its description and testing since DP 1.4 over USB-C became available.  And it's slightly more expensive.  But I've had solid experiences with both Cable Matters and Anker, so just in case you need another option to test, I figured I'd share it.

@jphughan Many thanks for taking the time to help.  I have an 0.8m Apple Thunderbolt 3 cable and this works without issues at home.  Problem is that I have hundreds of Lenovo 1m and 2m USB-C "docking station" cables in the office that don't work with the X1C7 or the 2018 rMBP.

I have ordered a bunch of generic 1m Gen 2 100W cables to see how the Dell monitor behaves with these cables and also a revised Gen 2 100W Lenovo cable.

I did not realise that the longer 2m Dell USB-C cables are Gen 1 but in the monitor sticky FAQ it mentions that Dell ship shorter / higher spec'd USB-C cables with their other monitors.

..and yes they made a typo with the Ghz - should be Gb.

Thanks for the Cable Matters recommendation.  I like the look of that cable as the plastic end is nice and short and not ridiculously long like other brands.

Can you think of any reason why these Lenovo USB USB-C cables do not work with the U3419W.  Remember they are designed to work with the USB-C docks that have separate 90W power.

@LMD75  happy to help, or at least try to.  As for the question about Lenovo cables, I really can't account for why they wouldn't function properly with an X1C7 if they do with a X1C6.  I think the X1C7 moved to Intel's newer Titan Ridge TB3 controller, whereas the X1C6 uses the older Alpine Ridge controller, but that shouldn't create a cable compatibility issue even if you were trying to use Thunderbolt 3 rather than USB-C, which it sounds like you're not.  The only other thought that crossed my mind is that Lenovo, like Dell, offers a USB-C docking station model that uses DisplayLink "indirect display" technology for video, in which case all data running between the dock and system would be USB data with no native DisplayPort Alt Mode traffic, but even if that's the dock you had, any cable that supports at least USB 3.1 Gen 1 should also be able to carry DisplayPort Alt Mode, and that still wouldn't account for why some systems work and others don't.

This might be one of those cases of a strange interoperability problem that shouldn't exist but does anyway.  They do happen.  For example, it's known that two older Dell XPS systems do not display video when connected via USB-C to Dell USB-C displays, even though those systems work fine with third-party USB-C displays and Dell's USB-C displays work fine with other USB-C systems.  And Dell's latest USB-C displays seem to be creating compatibility fits for MacBook users, for reasons that still aren't fully clear.  I realize that isn't a very satisfying answer and doesn't provide any reassurance that any particular solution actually WILL work as opposed to just knowing that it SHOULD work, but unfortunately those types of situations exist, and since I haven't tested the specific hardware combination you're trying to run, I can't provide any confirmation of a known working solution.  Sorry!

I just ordered a revised Lenovo 1m USB-C 20V/5A 100W 10Gbps cable and it worked for a couple of minutes then the screen blanked and came back up.  A few minutes later it had handshaking issues again.

Specs are here:

https://www.lenovo.com/us/en/accessories-and-monitors/cables-and-adapters/cables/CABLE-BO-USB-C-Cable-1m/p/4X90U90619

Still don't know why these Lenovo cables do not work properly.

I also ordered a bunch cheaper various branded cables and am now testing them for longer periods. 

My other 1m USB 3.1 Type-C Gen2 5A With E-Mark (Differential Pair) cables work fine so the problem is just with these Lenovo cables.

Does anyone know the exact specs of the Dell MRTCD 1m Type-C to Type-C that bundle with some Dell USB-C monitors?

Hi the MRTCD cables are USB 3.1 Gen 2