Replacement USB-C <> USB-C (5400 <> U2520D)

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@lindros2  I don't have a 5400, but I've used a 7400 and have not had any problems charging over USB-C.  It uses the USB Power Delivery standard like practically every other laptop that supports USB-C charging.  There are some more specialized laptops like the XPS 15 and Precision 7000 Series laptops that support 130W over USB-C (more than the official USB PD spec) and charging via two USB-C/TB3 ports simultaneously for even higher wattage, respectively, but that wouldn't come into play here.  I would expect that a Latitude 5400 would be designed for either a 45W or 65W power source, in which case if you want to charge from a display with built-in USB 3.x ports, then you'd need a USB-C cable that supports up to USB 3.1 Gen 1 (or Gen 2), DisplayPort Alt Mode, and USB Power Delivery up to either 60W or 100W.  Cables that support USB 3.1 Gen 2 (10 Gbps) are currently limited to 1 meter / 3.3 feet, such as this one.  If you're fine with USB 3.1 Gen 1 (5 Gbps), then this one that's 6 feet should work.  Both support DisplayPort Alt Mode (the former up to DP 1.4, the latter up to DP 1.2, which is fine for your display's resolution) and USB PD up to 100W.

@lindros2  The 5400 should always be using 20V -- some Dell laptops also support 15V, but to my knowledge they all support 20V.  That means that for a laptop, different wattage levels would be due solely to different amperage levels.  A 100W cable is technically rated for 5 amps and a 60W cable is rated for 3 amps.  This is because carrying higher voltage levels doesn't place any special requirements on the cable, but carrying higher amperage does -- but most consumes don't know how many amps their laptop requires.  They just know the total wattage, and thus many cables are rated in terms of max wattage, calculated based on USB PD's current max voltage of 20V.

@lindros2  What is the indicated wattage output of the power supply that shipped with your 5400?  And if you go into either the BIOS Setup or Dell Power Manager (if you have the latter installed), somewhere you should find an area that indicates the identified wattage of the attached power source.  What does that show when you use the included cable compared to any other USB-C cable you've tested?  On older Latitude systems, this information was in the "Battery information" section of the BIOS Setup, but I believe the 5400 got a BIOS interface redesign, so that might not be the case anymore.

Thank you again @jphughan 

again, this is super odd. The 5400 *requires* more than 61W - I’ve unfortunately proven it “non-scientifically”.

That is, the 60W/3A calculation (AmazonBasics cable) just doesn’t do the trick with the Dell. It will drive video, but throws the low charge warning. Not so on my Mac - it’s fine  

I’ve ordered three more cables and will report back. Just wish I could figure out what Dell shipped with  

(Note - the source remains the same - U2520 display powering the notebook - which pushes either 90W or 100W out the USB-C)

Thanks @jphughan @and @DELL-Cares 

Here’s the thing - it’s not wattage, but amperes - and PD flavor of the cable. 
the other cables don’t work regardless of 65W, 85W, 96W... power bricks. 
My chromebooks, ThinkPads, MacBook Pro, and other computers are less sensitive. 
the 5400 is very finicky..

@jphughan 

A very, very funny question you ask. I’ve looked all over Dell’s site, and can’t find any data on this. 
Looking at the slim power adapter, it’s a 90W/19.5V/4.62A unit. 
Overkill? The 5400 is simply an i5, so this isn’t a beast...

re BIOS - no dice - it’s a corporate managed device. Can’t get in. 

@lindros2  Some Dell systems ship with different wattage power supplies based on the CPU you ordered and/or whether your configuration includes a dGPU.  But that typically applies with Latitude 15" systems where that type of choice is offered.  A 14" Latitude 5000 Series probably doesn't even offer the higher performance 45W H Series CPUs or a dGPU at all -- but since you mentioned it was issued by your employer, they may have simply standardized on 90W power adapters or had one of those closer at hand.  Or actually, I just went to the Latitude 5400 configurator on Dell's site, and on the configuration I chose, I noticed I was given a choice between a 65W and 90W adapter.  Typically when a choice is offered, it means the system will function at full performance with a 65W source, but will charge the battery faster with a 90W source, the tradeoff of course being a larger and heavier power supply.

One way to tell what your specific system is designed for would be to deliberately connect an undersized power source and boot the system, at which point you should see a warning message saying, "You've attached a power supply of X wattage. This system is designed for Y wattage for optimal operation."  But the reason I say "should" there is because that "adapter warning" can be disabled in the BIOS, so if that was done and you don't have BIOS access to re-enable it, then you might not see that warning even with an undersized power source connected.

All that said, it seems that your system is designed for at least 65W for proper functioning, and in order to run anything above 60W/3A over USB-C, you need a cable rated for 100W/5A.  The vast majority of USB-C cables are only rated for 60W/3A, and there's nothing between that and 100W/5A.  And if you use a cable that's only rated for 60W/3A, then that is the most you'll get, even if the power source can provide more and the system being charged would benefit from more.  The reason is that in order to carry more than that, the USB-C cable needs to have an "e-marker" chip embedded into it that explicitly confirms that it is rated to carry higher wattage.  An e-marker is also required for USB 3.1 Gen 2 support.  I've personally run this test with 65W and 90W USB-C adapters.  When I use a 60W/3A cable, the system only detects a 60W power source.

So if the cables you've been testing with have all only been rated for 60W, then that's probably your issue -- and if your display supports providing up to 90W, then the cable it shipped with would have been rated for 100W/5A.  But the cables I linked in my first reply both support 100W.

(If you find yourself with a bunch of spare time, I actually wrote an explainer post about the various differentiators of USB-C/TB cables here.  I also did one for the various operating modes of USB-C/TB3 and their impact on possible display setups, as well as one covering the various TB3 security levels, and actually another one about Dell laptops and third-party USB-C power sources, which come to think of it you might find relevant too, albeit not with your U2520D display.  That thread is here.)

@lindros2  One other note: Since you mentioned that you have Macs that aren't complaining with the other cables, that doesn't necessarily mean that they aren't affected by a reduced wattage situation.  They might simply not be throwing a "slow charger" alert the way Windows is doing on your Latitude.  But you also didn't specify what Macs you have, so it's tough to say.  I believe that macOS has some area that will show you the wattage of the attached power source, or the wattage level it's using.  That distinction can be important because for example if you have a Mac that only requires a 60W power source, then it might only report 60W even if more is available.  But in that case, it might well be fine with a 60W cap introduced by a 60W/3A cable and might simply not bother griping about 60W vs. 61W.  (No idea why Apple felt the need to do that.  Same with their 29W power source rather than 30W.)  As an example, my Latitude 7480 is designed for a 65W power source, but it doesn't complain when a 60W USB-C source is attached, even though it WILL complain if I only use a 30W source.  But I just set up a friend with an Inspiron system also designed for a 65W source, and it DOES complain when a 60W source is used.

But the bottom line here is that the underlying cause of your experience here may not be that your Latitude is pickier than your other devices in terms of cables.  It might simply be that a) it requires more power than the other systems you're testing with, and/or b) it's will more readily complain about an undersized power source than the other devices you're testing with.  But if it's the latter, then the other cables you're using that seem to be limiting available power could be adversely affecting the performance of other devices you're testing with if they're designed for more power, even if they're not complaining about that situation.

See what happens when you get a cable rated for 100W, video/DisplayPort Alt Mode, and USB 3.1 Gen 1 or 2.  I think you'll find that this all goes away.

What drives me nuts is that I know this well - I used to work for Intel (CPU side) and write for trade mags (including reviewing Dell/EMC/Vmware - no more).

Back to this topic. Unfortunately - welcome to 2020 - Win10 doesn't tell you sh_te about what's wrong. Everything other than the OEM Dell power adapter and the Dell-supplied cable E5400 <> U2520D throw the "slow USB charger" error (with equally unhelpful Microsoft help page - not Dell).

The cables I purchased - on Amazon, Monoprice, and at Fry's and Micro Center - all say 100W (actually, that's not entirely true - one of them was 60W, but it was a cool right-angle version... that didn't work at all).

@jphughan 

I actually did note my Macs, but the stupid Dell forum (Lithium? custom?) threw an error and I lost the entire post. See below this post.

I have four USB-C MacBooks in my house (in addition to Samsung Chromebook 12" and ThinkPad 480s / ThinkPad X1 Carbon):

- 2017 MBP 13" (61W)
- 2018 MBP 15" (87W)
- 2019 MBP 15" (87W)
- 2019/2H MBP 16" (96W)

None throw "slow charging" (on the Dell E2520, that is), and complain less (not at all) using the other cables. I have battery apps (i.e. Coconut Battery, Disable Turbo Boost Pro, etc.) that will show real-time charge data.

FINAL comment - the only thing worse than the Dell 5400 is a Nintendo Switch. I had to order a genuine power cable to power its dock (Switch > Dock > TV). It has a weird 15V/2.6A requirement that nothing can "match".

The Anker and Aukey cables failed across the board - they're 60W charge-only.