How to check heat-related slowdown on USB-C power

Your laptop feels slower when it is plugged into a USB-C charger or dock, especially after a while. Heat could be part of the problem, but USB-C power, an external display, and power settings can also change performance.

Use the Overheating Test to see whether performance drops during a short period of heavy work. Then compare the laptop on USB-C power and on battery, keeping the test conditions as similar as you can.

Compare performance on USB-C power

Place the laptop on a hard, flat surface. Make sure its air vents are clear, then close games, video calls, and other heavy apps.
Open the Overheating Test on the laptop you want to check. Note whether it is connected to a USB-C charger, dock, or both, and whether an external display is connected.
Run the test for a few minutes. It puts the processor under full load and checks whether it slows as the device gets hot. Stop if the laptop becomes unusually hot, shuts down, or shows a temperature warning.
Let the laptop cool back down, then repeat the test with the same setup except for the USB-C connection you want to compare. For example, compare the charger connected with the charger disconnected. Keep the room, screen brightness, apps, and power mode as consistent as possible.
Compare the results and note any change in fan noise, warmth, or responsiveness. If the laptop has to run on battery for the second test, make sure it has enough charge and remember that its power mode may change when unplugged.

For a more useful comparison, change one thing at a time. If you unplug the dock and charger together, you will not know whether the difference came from charging, the dock, or an attached display. You can also compare the laptop with the dock connected but an external display disconnected.

What the result means

Performance drops as the laptop heats up

The test found a slowdown under sustained load, which is consistent with thermal throttling. Thermal throttling is when a device reduces its speed to limit heat. It does not prove that the USB-C charger caused the slowdown, since the test also heats the processor on its own. Check whether the same drop happens in both power conditions.

The laptop slows down only with USB-C connected

Heat is one possibility, but not the only one. A dock may add work for the graphics processor, especially with an external display. A charger with limited power output may also affect performance, and some laptops draw from the battery under heavy load even while connected. Check the charger's rated output and the laptop maker's guidance for compatible chargers.

There is no clear slowdown

The test did not find a noticeable drop during this short run. That does not rule out problems during longer workloads, in a warmer room, or with a particular app or dock. If the slowdown happens only during video editing or gaming, compare the same task in both setups and check whether it starts after the laptop has been working for a while.

The result changes between repeated runs

Small differences can come from background activity, battery level, room temperature, or a change in power mode. Let the device cool between runs and repeat each setup. A browser test is a practical comparison, not a precise temperature measurement or a diagnosis of a specific component.

How to reduce heat or rule out power settings

Improve airflow. Use the laptop on a desk rather than a bed, blanket, or soft cushion. Keep the vents clear and leave space around the sides and back.
Check the power mode. On Windows 11, open Settings › System › Power & battery › Power mode and use the same setting for both comparisons. On macOS, check System Settings › Battery › Low Power Mode and keep the setting consistent. Power modes can affect speed as well as heat.
Test without the dock's extra load. Disconnect external displays and other dock devices, then repeat the comparison. If the laptop runs cooler, reconnect devices one at a time to find what changes the result.
Use a suitable charger and cable. Check that the USB-C charger supports the wattage recommended for your laptop. A cable or charger that can supply less power than the laptop needs may limit charging or performance. Use a known-compatible charger for comparison.
Close demanding apps. Pause video exports, games, cloud backups, and large downloads before each test. These can add heat or make one run slower for reasons unrelated to the USB-C setup.
Clean and update carefully. If vents are visibly clogged, follow the laptop maker's cleaning instructions. Check the maker's support guidance for relevant system or dock updates, and avoid running repeated full-load tests while the laptop is already very hot.

When the laptop may need service

If it becomes unusually hot during light use, shuts down, or repeatedly slows down with clear airflow and a compatible charger, stop stressing it and contact the laptop maker or a repair shop. A fan, cooling system, battery, or power connector may need attention. Do not open a device that is under warranty unless the manufacturer says it is safe to do so.

Why USB-C can change the comparison

USB-C is a connector, not a guarantee of one charging speed or power level. A dock can also connect displays, storage, and other devices, adding work or heat. To separate these effects, compare a direct charger connection with the dock connection, then compare both with and without the external display. For a broader guide to testing a laptop for heat-related slowdown, see How to test whether heat slows your laptop.