Low charge rate for PD on Thunderbolt USB C. Dell Latitude 7490

[theyoyomaster]

Ubuntu Version:
Kubuntu 25.10

Desktop Environment (if applicable):
KDE Plasma

Problem Description:
I have a Latitude 7490 that I primarily run Kubuntu on but dual boot to Windows 10 for a few things that can’t be done on Linux. I’ve had it for about a year and a half and am finally getting comfortable in the environment but still am working to learn the higher level stuff. I recently had to replace my laptop due to tornado damage but was able to save the hard drive and swapped it into an identical refurbished one from the same vendor where I got my first one, except this one has a thunderbolt port. It’s a super nice option and I would love to ditch the barrel plug for charging but for some reason it is limiting the charge rate in Kubuntu to 40 watts. I have one of the new smart chargers from Anker and can see exactly what wattage, amps and voltage each device is drawing. During post and in Windows it draws 60 which is what the barrel plug delivers (apparently there’s a 90 watt barrel plug option and Dell’s documentation says TB3 can go up to 100 but I’d be happy with 60).

I’ve been digging around and can’t find anything that would limit the negotiation in Linux, but since I can literally see it charging at 60w until the login screen pops up and then drop to 40w it’s pretty obvious that something software related is limiting it. I tried updating the Bios and TB firmware but nothing changed on charge rate. Anyone have an idea of how to start tracking this down?

Oh, also I cannot get these forums to load on my laptop in Firefox. I disabled my vpn and all adblocks but it just hangs and says connection timed out.

[marcelstevano]

The 40W cap you’re seeing on the Latitude 7490 is a classic case of the Linux kernel’s typec and ucsi_acpi drivers failing to re-negotiate the Power Delivery (PD) profile after the initial BIOS/POST phase. Since you’ve already verified it pulls 60W during boot and in Windows, we can focus on the software negotiation in Kubuntu.

1. Kernel Parameter Workaround

Many Latitude users have found success by forcing the ACPI interface to identify as a newer version of Windows, which changes how the firmware exposes power resources to the kernel. Try adding this to your GRUB parameters:

Open terminal and run: sudo nano /etc/default/grub

Find the line: GRUB_CMDLINE_LINUX_DEFAULT=“quiet splash”

Append acpi_osi=“Windows 2020” or acpi_osi=! (Note: try the 2020 one first).

Run sudo update-grub and reboot.

2. Power Management Conflicts

Since you are on KDE Plasma (Kubuntu 25.10), check if power-profiles-daemon or tlp is conflicting.

If you have TLP installed, check /etc/tlp.conf for any START_CHARGE_THRESH settings that might be interfering.

Try temporarily stoppip power daemon to see if the rate jumps back up:

Try temporarily stopping the power daemon to see if the rate jumps back up:

sudo systemctl stop power-profiles-daemon

3. Debugging the PD Handshake

To see exactly what wattage the kernel thinks it’s allowed to pull, check the power supply class:

cat /sys/class/power_supply/AC/uevent (or similar path like BATO)

Look for POWER_SUPPLY_ONLINE=1 and check if there’s a limit reported in microamps/microwatts.

Regarding your Firefox/Forum issue:

If the forum hangs on “connection timed out” despite disabling VPN/Adblock, it sounds like a MTU (Maximum Transmission Unit) mismatch or a DNS resolution hang specific to that interface.

Try lowering your MTU temporarily: sudo ip link set dev <your_interface> mtu 1400

Alternatively, check if systemd-resolved is struggling. A quick ping -c 4 will tell you if it’s a DNS or a routing issue.

[theyoyomaster]

Thanks for the very detailed reply. So the issue with the forums page cleared up after a day or so, not sure why but I didn’t change anything on my end and it even works with my VPN now.

For the power stuff, I realized my testing was flawed. I think it’s great to get the info you shared out there for others in similar situations, but I missed on key aspect of just measuring wattage going into the laptop. The battery itself appears to only charge with 40w in both Windows and Linux and everything above that is to run the system. Where the discrepancy came from is that Windows is more resource heavy so it always needed an extra draw. When I was staring at the readings and not touching the laptop in Linux it would drop down to the battery charge limit of 40w but when I booted up Plex or something it would jump to 60w or more.

[peterwhite23]

@marcelstevano

Try lowering your MTU temporarily: sudo ip link set dev <your_interface> mtu 1400

FWIW, MTU should be set to 1320, according to a message by @Wild_Man in the Ubuntu Community Matrix room. It may not be necessary anymore, though. It was some kind of DDoS mitigation that created some collateral damage.