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November 9th, 2019 15:00
Understanding Dell laptops and USB-C power sources
(UPDATE: Since writing the post below, it seems Dell may be changing its 65W max power draw limit from non-Dell USB-C power sources. I've seen reports from owners of the XPS 15 9500 (released in 2020) indicating that it will draw at least 90W from non-Dell sources. But what I wrote below would still be true for most of the Dell laptops in use as of this update in July 2020. Original post below.)
I decided to write this post because there seems to be a fair amount of confusion around Dell laptops and USB-C power sources, particularly third-party USB-C power sources, including how to determine what wattage the system is drawing from them and why power sources are identified a certain way. Hopefully this will help Dell laptop users understand how to learn more about how their setup is working and why it's working a certain way.
First off, most if not all recent Dell systems will display an AC adapter wattage readout in their BIOS Setup interface under the Battery Information section, specifically below the battery graphic. You can access your BIOS Setup by pressing F2 during initial startup. When using non-USB-C power sources, i.e. Dell-specific AC adapters that use a barrel-style connector, the wattage shown there will be the detected wattage of the AC adapter, even if it's more wattage than the system will actually use. So for example if I plug a Dell 130W AC adapter into an XPS 13 9350 that's only designed for 45W, it will still identify the power source as 130W, even though it will never actually USE that much wattage. Using a Dell adapter that can provide more wattage than the system needs will not damage the system in any way. I've kept a Dell 130W AC adapter in my living room for years and have used it with Dell systems designed for anywhere from 45-130W and it's been fine.
With USB-C power sources, the wattage readout you see there is a bit more complicated. The reported wattage will be the maximum wattage that particular system will actually draw from that particular power source. That might sound simple enough, but it isn't quite so simple, partly because of a restriction around USB-C charging that I've found implemented on multiple Dell systems. Basically, as of this writing, multiple Dell laptops I've tested will not draw more than 65W from a non-Dell USB-C power source, even if the power source can provide more wattage and the system is designed for more wattage and would therefore benefit from drawing it. In addition, the USB-C cable you use can matter. USB-C cables that support USB Power Delivery are available in two versions: up to 60W (sometimes written as 3A, or amps) and up to 100W (sometimes written as 5A). The latter are typically thicker in order to carry the extra power safely. The relationship between watts and amps here is based on the current 20V max of the USB PD spec. Citing amps is technically more precise because the higher amperage requirement is what drives the need for thicker wiring, but most customers think in terms of wattage. Anyhow, if you use an "up to 60W" cable, you will never get more than 60W, even if you have a USB-C power source that can provide more wattage and a system that would otherwise draw more.
So let's look at some examples. All of these assume USB-C power sources (as opposed to the barrel-style Dell AC adapters) and that you're using an appropriate cable for the wattage involved. They also assume that you're using a USB-C source that can supply 20 volts. Some lower wattage sources only supply power up to 15V, and although some laptops will work with such sources, others will not. I didn't test such chargers.
Case #1: An XPS 9350, which is designed for 45W. If you connect a 30W power source, the system will show 30W since that's all that's being offered. If you connect a 60W power source, it will show 45W because that's the most the system is designed to draw.
Case #2: A Latitude 7480, which is designed for 65W but will take advantage of 90W when available. If you connect a 30W source, it will show 30W. If you connect it to a 65W source, it will show 65W. If you connect it to a Dell dock that can provide up to 90W, it will show 90W. But if you connect it to a non-Dell 90W power source, it will show 65W, even though other non-Dell systems will correctly show that power source as 90W.
Case #3: An XPS 15 9570, which is designed for 130W. That's actually more than the official 100W max of the USB Power Delivery spec, but Dell has done something proprietary on this and some other 130W systems and certain docks (like the WD19TB) to stretch that spec to allow carrying 130W over USB-C. They also make a 130W USB-C power adapter. If you connect this system to one of those devices, it will show 130W. But if you connect it to a non-Dell 90W power source, it will still only show 65W. This is frustrating because this particular system would actually perform better if it drew 90W rather than 65W and is still refusing to do so. In addition, I believe (but have not confirmed independently) that the XPS 15 models will not work at all with any USB-C sources that supply less than 60W -- although even a 60W source would be inadvisable overall. Battery charging will be slow to non-existent and CPU and GPU performance throttling would be significant as the system attempted to operate within the constraints of a power supply that offered less than half the wattage it the system was designed to use. A 60W source would be fine to use purely for battery charging while the system was asleep or off, but would not be a great choice while actually using the system.
Hopefully this helps people understand how Dell systems identify and work with USB-C power sources!
ITPRO_AZ
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February 11th, 2021 08:00
I have a M17 R3 2021 Dell Laptop and it has the USB-C port.
I have 2 issues
issue 1 - if i have my docking station (USB-C) plugged in and the barrel charger, it uses the dock to charge the laptop. This causes the laptop battery to drain. once it gets low, the computer shuts off. This trips the safety's on the USB-C so it stops working.
The fix for the USB-C not detecting devices - I have to go into the bios and reset the USB-C connection to fix it.
Issue 2 - Can't use dock and power supply together, so is there a way to disable the USB-C charging so i can use the dock and still have the AC Adaptor charge?
Thanks,,
John - AZ IT PROFESSIONAL
jphughan
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February 11th, 2021 09:00
@ITPRO_AZ I'm not sure what's going on with the device detection issue, but you shouldn't have to do anything to have the system charger from the barrel style connector. Before Dell introduced USB-C/TB3 docks that could provide up to 210W of power (by plugging into two USB-C/TB3 ports), their guidance to people who were using USB-C/TB3 docks with high-powered systems like the Precision 7000 Series models was to connect the barrel-style connector alongside the dock, and it worked fine. That's also the guidance for people using systems like the XPS 15 (130W) with third party docks that don't provide that much power. Are you sure your barrel-style adapter is operating properly? I'm not sure if Alienware's BIOS interface works like what I'm about to describe, but on Latitude and XPS systems, if you go into the BIOS Setup and click the Battery Information section, the system shows the wattage of the detected power source. If you do that while only your barrel charger is connected, does the system identify the correct wattage for that power supply? And is that power supply correct for your system? If that all looks good, then I'm not sure why your system isn't using that as its power source when both are connected.
Tyre Reviews
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February 14th, 2021 11:00
Just to bring this full circle, I flew with the recommended ravpower adaptor and it was great.
You can't edit super hard on a flight so there was hardly any battery drain (I have the 97w battery and the laptop only accepted 65w of charge from the adaptor), and even with a small bit of drain, it topped up fairly quickly when doing lighter work.
Thank you again for the recommendation
jphughan
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February 14th, 2021 12:00
@Tyre Reviews Excellent! Thanks for reporting back and glad I could help.
chrisd015
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March 12th, 2021 19:00
Lots of useful info here. Just makes me wonder why Dell here in Australia supplied a 30W charger with my XPS13 9365 instead of a 45W charger. Unsurprisingly I have frequent random problems with USB devices despite using a Dell DA200 dock.
dejo_zg
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April 2nd, 2021 02:00
Hi, I plan to buy a larger amount of XPS 9500 with i9-10885H processor in combination with Dell U2421E monitors. I also plan to use U2421E as a power source for XPS. I have bought one piece of each for testing purposes before I jump into the larger purchase.
The power adapter of XPS is 130W while U2421E monitor can provide only 90W of PD. When I connect them via USB-C port, I got the warning in windows that the slow charge is active. I've done some performance testing of CPU, RAM and disk with PassMark's PerformanceTest tool, and the results are the same whether the XPS is powered by the power adapter or by the U2421E monitor. As laptops will be used by developers, I will test the performance with them as well.
Is there any other way to tell if XPS performance will be degraded if powered only by U2421E monitor (90W)?
jphughan
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April 2nd, 2021 06:00
@dejo_zg With the XPS 15 9500, Dell tweaked things slightly compared to previous XPS 15 generations. If you order the system WITHOUT an NVIDIA GPU, then the system is designed for a 90W source. If you order it WITH an NVIDIA GPU, then it’s still designed for 130W. So I would suggest using a benchmark that specifically stresses the NVIDIA GPU, like 3DMark. You also might notice slower battery charging even when not running the NVIDIA GPU, but I’m not certain about that since I don’t have direct experience with that setup, and that may not be important to you anyway.
jphughan
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April 5th, 2021 20:00
Hey @hazelnutz, glad you found it informative. The Precision 5540 is the sister system of the XPS 15 7590, and while I can't remember for certain if I saw positive confirmation one way or the other, I'm pretty sure I remember seeing that it has the same 65W limitation. The first XPS 15 model that I've seen confirmed to allow more than 65W is the subsequent generation XPS 15 9500, which is the sister system of the Precision 5550. Again I don't know for certain, but I personally wouldn't be optimistic. Sorry!
hazelnutz
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April 5th, 2021 20:00
Hi jphughan,
This is a very interesting article and it's the exact question that I've been trying to find answers to for some time. I have a Dell Precision 5540 which requires 130W. Just like to check if the limit of 65W also applies to this model?
hazelnutz
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April 6th, 2021 00:00
Hi jphughan,
Thanks so much for the quick response! It's a shame that dell has put in this restriction on 3rd party USB-C power adaptors. Guess they want us to buy Dell peripherals.
Tyre Reviews
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April 15th, 2021 13:00
One more update. I liked the 90w solution to my flying issues so much, I bought a UK Version too. This one:
https://www.amazon.co.uk/gp/product/B08SWF5J6D/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1
I just exported a big video in premiere while using this adaptor to see what battery drain I'd actually get.
30 minutes of flat out CPU and GPU usage, I left the screen on, there was something running via USB, and the battery just drained 6% in that half an hour.
Tyre Reviews
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April 15th, 2021 13:00
One more update. I liked the 90w solution to my flying issues so much, I bought a UK Version too. This one:
https://www.amazon.co.uk/gp/product/B08SWF5J6D/ref=ppx_yo_dt_b_asin_title_o04_s00?ie=UTF8&psc=1
I just exported a big video in premiere while using this adaptor to see what battery drain I'd actually get.
30 minutes of flat out CPU and GPU usage, I left the screen on, there was something running via USB, and the battery just drained 6% in that half an hour.
jphughan
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April 15th, 2021 19:00
@GTlisboa Most USB-C cables are limited to 60W. If you use those cables, then 60W is the maximum power you can get from a charger, even if the charger can provide more power and the laptop would use more. You need to get a USB-C cable that supports up to 100W instead, and then your laptop will be able to receive 65W. If you are getting a docking station, some of them include an appropriate cable. But if your docking station will not include a cable, then if you get a regular USB-C docking station, you will need a USB-C cable that supports 100W and video. Not all USB-C cables support video. And if you get a Thunderbolt 3 docking station, you will need an actual Thunderbolt 3 cable that supports 100W.
GTlisboa
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April 15th, 2021 19:00
Hello, how are you?
First off, thank you very much for the post, the informations here are very helpful.
I'm very new to this thing and english is not my first lenguage so I didn't understand a lot of what was said in the discussion. Can someone please help me out?
I own a Dell Inspirions 14 that requires 65W. I already tested charging it with a "non dell usbc" and it displays on the screen that I dont have enough power. At this point I'm thinking it is probably because of the cable, because the power brick is more powerful than that.
The thing is, I want to buy a third party docking station and use 1 usbc cable only to power the whole thing in my laptop (it has a thunderbolt 3.0). Will I be able to do it if I have the proper power brick and cable? Or will it keep displaying the same message again?
Thank you very much for the help.
GTlisboa
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April 15th, 2021 20:00
The dock comes with the cable to connect to the laptop, but not the one to power it on, i will have to just buy one then.
Anyway, thank you very much for the quick response, you were very helpful