Your laptop charges slowly over USB-C but quickly on the barrel plug almost always because the USB-C source delivers fewer watts. The USB-C charger may be rated lower than your original adapter, the cable may not carry enough current, or that specific USB-C port may only support data and low-power charging. The barrel charger is the manufacturer's full-wattage supply, so it always wins.
Why this happens
Charging speed comes down to watts (volts multiplied by amps). Your barrel charger is sized exactly for the laptop, so it delivers the maximum the machine can accept. A USB-C charger only matches that if every link in the chain supports it.
- The charger is lower wattage. A 30W or 45W USB-C charger cannot match a 90W or 135W barrel adapter, so the laptop charges slowly or only maintains its level while in use.
- The cable is the limit. Basic USB-C cables carry up to 3A (about 60W). Higher power needs an e-marked cable rated for 5A (100W) or a newer 240W cable. A weak cable caps the whole connection.
- The port is not full-power. Some laptops have one USB-C port for charging and others that only do data or low wattage. Plugging into the wrong port limits charging.
- Power negotiation failed. USB Power Delivery negotiates a voltage step (for example 20V). If the charger and laptop cannot agree on a high step, they fall back to a slower 5V or 9V profile.
Is this normal?
Yes. It is completely normal for a lower-wattage or third-party USB-C charger to charge more slowly than the original barrel adapter, because it simply supplies less power.
Does it cause any problems?
No, slow charging does not damage the laptop or battery. The only downside is a longer charge time, and if the charger is far too weak the battery may drain while you use the machine under heavy load.
How to fix or check it
- Read the wattage printed on both chargers. Compare the output figure (for example 20V 3.25A equals 65W) to see how big the gap is.
- Use a USB-C cable rated for the power you need. For above 60W, use an e-marked cable that lists 100W or 240W support.
- Plug into the correct port. Check the laptop manual or look for a small power or lightning-bolt marking next to the USB-C port that supports charging.
- On Windows, hover over the battery icon or open Settings and look for a message like "plugged in, charging slowly," which confirms low input power.
- On a Mac, hold Option and click the battery menu, or open System Settings and Battery, then check the power adapter wattage being drawn.
- Match or exceed the original wattage with a USB-C Power Delivery charger to get full speed.
Frequently asked questions
Can I damage my laptop by using a lower-wattage USB-C charger?
No. The laptop only pulls what the charger can safely provide, so a weaker charger just charges slower and cannot overload the machine.
Do I need the exact same wattage as the barrel charger?
To charge at full speed, yes, match or exceed it. A higher-wattage charger is fine because the laptop draws only what it needs.
Why does it say charging slowly even with a big charger?
Usually the cable is the bottleneck. A cable rated for only 3A limits high-wattage charging, so switch to an e-marked 5A or 240W cable.