U2721DE, which 'all-in-one' USB Type-C cable?

Question

Hello

I have a Precision 3551 station (USB-C Thunderbolt port) and a U2721DE monitor (USB-C, USB, RJ45...).

With the stock USB-C male-male cable (that came with the screen), I have a very convenient all-in-one setup: everything is plugged to the monitor, and a single cable carries power (65W), network (from rj45), video, and connection to USB accessories.

The only issue is that the cable is too short, about one meter. I tried a female-male extension cable (one meter), that is claimed to be compatible with 100W power supply, 10 Gb/s data, Thunderbolt 3, alt DisplayPort, and more. But it doesn't work, the video signal is not transmitted.

Is the cable bad quality? Should I try with a two meter male-male cable? Or do I need additional cable characteristics?

Geronimo · Answer

I just realized that the USB-C port of the monitor is not TB, it transmits the image with alternate DisplayPort, correct ? So the problem would not be the TB compatibility

samus1 · Answer

Is a 'Precision 3551 station' a docking station for your laptop? If do have your monitor connected to your laptop over Thunderbolt, just be aware that relying on it as the sole power source can/may/will reduce performance, since your laptop most likely requires more than the 90W that a TB3 is cable of (i.e. an XPS requires 130W). The 2 meter Razor Thunderbolt 3 cable I purchased was 59.99, so they aren't cheap. I'd try to find an OEM Dell one as cheap as possible (call and see if you can get any kind of discount). I purchased the Razor cable for an eGPU (that I sold, the massive performance loss is not worth it at all).

Geronimo · Answer

Thanks for your answer.

No the Precision is a (big) Dell laptop, a so-called 'mobile workstation'. The monitor itself plays the rôle of a docking station: everything is plugged once for all to the monitor, and everything is transmitted to the computer via the USB-C cable.

Your're right that the 65W output of the monitor is a bit short for the laptop, but in practice it works if I disable the powerful graphics card (that I don't need anyway).

Everything works well with the stock ~1m Dell cable, so I'm just looking for a ~2m alternative.

jphughan · Answer

@Geronimo Extension cables are always tricky. Even if each individual cable in a chain is rated to support a certain spec, that doesn't guarantee that the entire assembly will. Obviously (or maybe not obviously?) you can't just string together an unlimited number of extension cables and expect your creation to maintain support for all of its various features. Electrical signals degrade with distance in a cable, and actually the transition between a male connector and a female receptacle is a significant source of degradation, to the point that a 3-foot + 3-foot assembly might not perform as well as a 6-foot single cable, because the latter avoids that extra connector to receptacle transition. (That source of signal loss is exactly why "active cables" are a thing. They incorporate signal booster chips on one or both ends of a cable to boost the signal immediately after the source signal crosses the connector onto the cable and/or just before it crosses the connector on the other end.)

All that said, this cable should work for you, since it works fine for me. It's only 1.8 meters rather than an even 2 meters, but if that's close enough, enjoy.

Monitors

U2721DE, which "all-in-one" USB Type-C cable?

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