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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!
jphughan
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April 15th, 2021 20:00
@GTlisboa Your reply does not make sense. There is not a separate cable to power a laptop on. Laptops only use a single cable to connect to USB-C docks or Thunderbolt docks. But if you want to be able to power on a laptop using a dock, then the laptop has to support that feature AND you need a dock that is designed to use that feature with your exact laptop model. Dell docks can power on certain Dell laptops, but typically Inspiron laptops do not support that feature at all, not even from Dell docks. Dell seems to offer that feature only on their business laptops, like Latitude, Precision, and XPS models. But if you buy a non-Dell dock, you definitely will not be able to power it on from the dock.
jphughan
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November 25th, 2021 04:00
@Hoinz_p Laptops and pretty much all devices with batteries for a long time now have incorporated circuitry to prevent “overcharging” a battery, so once a battery reaches 100%, it will only draw a tiny amount of power to remain topped up. But if you are concerned about batter longevity, you may want to read my post marked as the answer in this thread, which discusses a configuration that will preserve your battery even more if you are willing to sacrifice some everyday convenience.
jphughan
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November 25th, 2021 04:00
@Hoinz_p Quick add-on to my previous reply. “Memory effect” doesn’t refer to keeping a battery charged to 100%. It refers to the behavior that with certain types of batteries, if you only drain them partway before charging them back up, then eventually that partway level will become their lowest possible charge level. Essentially the battery “remembers” that as its lowered charge level. But that applies to nickel cadmium (NiCd) batteries. Laptops and many other electronics switched over a long time ago to lithium ion (Li-ion) or lithium polymer, and those battery chemistries do not exhibit “memory effect”.
Hoinz_p
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November 25th, 2021 04:00
Hello,
I am owning a Latitude 5480 device and connect it to a HP G2 dock via USB C.
It works fine, so USB 2 and DVI all these interfaces (except for the on/off button which seems to work with HP notebooks only).
My Question: Is the Dell device charged all the time (as long as its connected) or is there any intelligence, that stops charging upon reaching the 100% ?
Otherwise, is there a way to NOT charge the Laptop while its connected to USB-C? Because I fear that the Capacity may decrease over time, if I am constantly charging the battery (Memory effect?)
Thanks!
Hoinz
Hoinz_p
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November 25th, 2021 09:00
Thank you @jphughan for the explanation. I will check my BIOS if it has options like you described in the other thread. Thanks again, Hoinz
snowmaen
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December 8th, 2021 21:00
Hi jphughan,
Thank you for the write-up, this thread has been very informative! I have an XPS 15 9560 I bought in Jan 2018 that can no longer charge with an AC adapter, due to an issue with the motherboard. Thankfully it can still charge from a USB-C source, so instead of replacing the MB I'd like to find a good USB-C power source that won't hurt the charger or my laptop in the long run.
Would you have any suggestions for finding a compatible USB-C power source for a 9560? It previously used a 130W AC adapter, and I've been charging it with a borrowed Apple 61W USB-C source while diagnosing the issue.
My understanding is that the 9560 will probably not support the Dell 130W USB-C charger, but if it also won't support third-party 130W USB-C chargers, I'm not sure what my best option is. Many of the forum posts on this topic that I've encountered are 2-5 years old, so I wonder if any of the more-recent USB-C developments (like Apple's new 140W USB-C charger) would work for my laptop? Otherwise, would you have any thoughts on the kind of adapter and/or cable I can safely look for?
Thank you so much for your time!
jphughan
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December 8th, 2021 21:00
Hey@snowmaen, glad I could help, and thanks for the kind words! In terms of your issue, the 130W output of Dell's 130W USB-C adapter is achieved via some proprietary method, since the USB PD spec at the time maxed out at 100W, so you won't find third party 130W adapters. As for Apple's 140W adapter, that is achieved using the brand new USB PD 3.1 spec, which defined power levels up to 240W. But the XPS 15 9560 wouldn't support PD 3.1, and in fact right now even Apple's adapter can only deliver 140W when paired with a MagSafe cable, because there are no regular USB-C cables that support the new PD 3.1 standard yet.
The only way I know of to get 130W into your system via USB-C/TB3 is with a Dell docking station that supports it, which would include the:
But unless you can find a great deal on a used dock or might want a docking station anyway, that would admittedly make for a fairly expensive power adapter, and would also be less portable than a regular power adapter. (And no, I have no idea how it's possible that the XPS 15 9560 can receive 130W from the WD15 and TB16 docks, and yet can't receive 130W from the Dell 130W USB-C adapter, even though that adapter launched after both the XPS 15 9560 and those docks. You would think the 130W AC adapter could have been made backward compatible with existing XPS 15 systems by doing whatever those docks do, but evidently not.)
Elio11
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January 22nd, 2022 09:00
I can confirm that my 2020 Dell XPS 15 doesn't charge at all with a less than 60 watt power supply while powered on or in sleep. Oddly enough it acctually will charge with a 45w power supply when powered off.
LiamJM
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February 7th, 2022 22:00
Thanks @jphughan for detailing this issue. Unfortunately, I didn't see this until after I backed a 3rd party GaN charger and battery on Kickstarter. Do you know if there has been any update on a fix for this? I know newer models don't seem to have this limitation, so it seems strange Dell hasn't patched it with a BIOS update. It's quite disappointing from Dell.
Peto Pedro
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February 8th, 2022 02:00
Hi
I have completely opposite problem with crazy latitude 3500
I have replaced like 3 motherboards and 2 batteries and tried 10 freaking dell genuine adapters 90w or 60w or 45w barrel connector charger and STILL this will not chare ???
I can't wrap head around how this can't determine wattage from GENUINE (still made in china) charger new motherboard two batteries both excellent health ! Replaced jack as well !
And if I plug any usb type -c adapter/ charger it simply charring ?? what the heck is going on here ????
Is dell crafty they doing this on purpose??
Same with HP laptops !! these brands going on my nerves ! This cheeky checking power absolutely doesn't exist on Asus or Ace or MSi best laptops! It is just made not to use non dell overpriced adapters .. so ppl will buy only dell ones..
If anyone knows why it won't charge .. let me know
thnx
jphughan
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February 8th, 2022 06:00
@Peto Pedro I don't know of any cases where a BIOS update increased the maximum power draw on third-party USB-C chargers. That doesn't mean it hasn't happened, since Dell has a lot of laptops out there, but in my experience it's pretty rare for Dell to implement "feature enhancements" like that to existing systems via BIOS updates. It's not completely unheard of, but I wouldn't hold my breath.
Peto Pedro
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February 10th, 2022 05:00
BIOS update is pointless so don't need to even do it ! in reality they don't absolutely do anything there will ad one little totally unimportant mostly security and that's all nothing benefitful bios updates brings whatsoever...
Oh you would be surprised all this fiasko is just money grab business that ppl won't use third party chargers.. All amerinkas companies do this for profit ..
ONly Asus ,acer and MSi are kind you can use third party..
Even I have genuine adapter like 10 of them and still power wattage pathetic dell can't determine !
What a loads of
And suddenly when I connected 90W adapter which isn't even fit or supplied for this laptop it will charge ...
SpektrTX
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March 9th, 2022 12:00
My problem is similar, and it's really irritating.
Dell XPS 9710, with four Thunderbolt 4 USB-C ports.
Comes with a 130 watt power supply.
This all above works fine.
However, I have two different USB-C docks/hubs. A sophisticated 60W Thunderbolt 3 unit; and a dumber USB-C Power Delivery hub.
The scenario occurs when I have the existing USB-C 130 W Dell power plugged in. AND then I plug any of the other hubs (only one at a time) into the USB-C port. They need power to run other USB-A devices, so I have to stick power to those things. The problem is that the Dell computer says "Oh, I have two simultaneous power sources, so I'll just use NOTHING and die in about four hours."
So if I use a seven year old USB-A hub, and connect power to it, and then to an adapter for the Dell XPS, all is good. But the USB-C hubs cause the Dell XPS to choke.
Any ideas on this one? It's sure to appear more and more often because people will start connecting docking stations/hubs to these things. Thanks for any input!
freddy_max
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March 27th, 2022 00:00
Thanks for the great explanation @jphughan.
I have an XPS 9510, Intel 11th gen, 3050Ti, 130W power. With that I use the Cable Matters USB-C hub with 100W PD: https://www.amazon.com/Cable-Matters-Multiport-DisplayPort-Ethernet/dp/B06Y5N3YCD/ref=sr_1_4?crid=2DQNSY5FH3DJM&keywords=cable+matters+displayport+to+usb+hub&qid=1648366063&sprefix=cable+matters+displayport+to+usbc+hub%2Caps%2C127&sr=8-4
In the BIOS it shows to deliver 85W. Will I run into throttling/ performance degradation? I don't mind slow charging.
ejn63
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March 27th, 2022 05:00
The answer is yes, you will see reduced performance; the system with the nVidia GPU cannot run at full speed on an 85W power adapter.
The battery will charge but you need the original adapter to run the system at full speed.