Whether you can use a USB PD charger with lower wattage than the original on a laptop that charges over USB-C depends on whose guidance you read. Apple says a Mac can charge from a lower-wattage adapter, while Samsung says charging becomes significantly slower or problems such as screen flicker occur, and advises using the original adapter.
Apple's Use a power adapter with your Mac (published July 6, 2026, Korean edition) says a Mac that charges via USB-C can charge from a USB-C power adapter or display with higher or lower wattage than the recommended adapter. The adapter must support USB PD, and third-party adapters must comply with applicable international and regional regulations and safety standards. The same page recommends using at least the minimum wattage of the recommended adapter for the best charging experience. The recommended wattage varies by model: on that page, MacBook Neo lists a 20W adapter, MacBook Air (2022 and later) lists 30W (13-inch model only), 35W, 67W and 70W adapters, and the 16-inch MacBook Pro (2021 and later) lists a 140W adapter. The troubleshooting page If your USB-C power adapter isn't charging your Mac laptop (published April 21, 2026) is a little firmer: you can use any USB-C adapter, but you should use one with equal or greater wattage than the adapter that came with your Mac.
You can check on screen whether the charger is too weak. According to Apple's Charge your Mac laptop computer (published September 16, 2026), macOS Tahoe 26.4 and later can show "Slow Charger" in the battery status menu and Battery settings when charging is slow. To see the actual wattage of the connected charger, hold the Option key, choose System Information from the Apple menu, and look under AC Charger Information in the Power section. Plugging chargers into two ports does not make it faster: a Mac charges through only one port at a time and uses the source supplying the most power.
Samsung Electronics Service's laptop battery charging guide (published December 5, 2024) says that using an adapter with lower power than the one supplied can make charging significantly slower or cause problems such as the LCD flickering, and that a lower-voltage adapter may cause abnormal behavior due to insufficient voltage. Its Galaxy Book6 charging guide (published March 16, 2026) says that using an adapter and cable other than those supplied can slow charging significantly, and that a pop-up appears at the bottom right of Windows if Samsung Settings is installed. Both Samsung pages advise charging with the original adapter supplied with the laptop (the Galaxy Book6 page also mentions the cable).
If the laptop does not charge at all after you switch chargers, check the cable too. Apple's troubleshooting page notes that some USB-C cables support only data transfer and will not charge a Mac. How a charger's wattage rating breaks down into voltage and current combinations is covered in our guide to choosing a USB PD charger.
This answer is limited to Apple's and Samsung's official guidance. Laptops from other manufacturers, and laptops that use round barrel-plug adapters rather than USB-C, were not checked. Neither manufacturer's pages say whether a lower-wattage charger affects battery lifespan. Check the recommended adapter wattage in your laptop's manual or on the manufacturer's support page.