Does the wattage of the cable need to be equal to or less than the wattage of the adapter? E.g., does a 60W USB-C charge cable require a 70W USB-C power adapter, or is it okay with a 30W adapter?
MacBook Air, macOS 13.4
You need to use a Power Adapter adequate to charge your Mac computer. When using a USB-C charging cable, the maximum power transfer between the Power Adapter and Mac will be limited by the cable.
As such, if the Mac requires less power than the charging cable is rated, all will be well. If the Mac requires more power than either the cable or Power Adapter is rated, charging will be limited to the lower of the the cable or power source power rating.
Also consider that battery charging will simply be slower than the maximum supported rate if the charging source is less than the maximum supported by your Mac.
In summary, you generally only need to consider the Power Adapter and charging cable if you need to charge the Mac at its fastest possible rate. Providing that each component is otherwise healthy, no harm will come to the Mac, charging cable or Power Adapter when charging over a USB-C connection.
DaisyB2005 wrote:
Does the wattage of the cable need to be equal to or less than the wattage of the adapter?
LotusPilot did an excellent job with their reply to you. I just wanted to add a bit.
In general, the power capacity of the cable should be equal or greater than the applied power through it ... however:
Apple cables (& many other top brands) typically employ "sensors," known as e-markers, to prevent passing through too much power. So, for example, if a power adapter can deliver up to 100W but the device can only safely handle 60W, the e-marker chip ensures that only 60W is delivered. That is why you should always use quality cables. Cheap cables may not include these sensors.
Tesserax wrote:
Apple cables (& many other top brands) typically employ "sensors," known as e-markers, to prevent passing through too much power. So, for example, if a power adapter can deliver up to 100W but the device can only safely handle 60W, the e-marker chip ensures that only 60W is delivered. That is why you should always use quality cables. Cheap cables may not include these sensors.
Almost...🙂
While certified USB-C cables incorporate the e-marker chips - and are involved in the Power Delivery handshake between source (power supply), load (the device being charged) and the cable - power is limited to primarily protect the cable.
The load itself regulates battery charging - the supply being limited by the cable and power source.
THANK YOU SO MUCH TO BOTH OF YOU! I lost my MagSafe adapter, I'm midproject with a deadline, my old laptops can't handle Word 365 (which I have to use as a freelance editor), and I don't have anything to charge my dead MacBook Air. Heading to the store now. 🙏🏼
And thanks for the info on avoiding cheap random brands. A friend was trying to steer me in that direction, but I recalled ruining a phone on a camping trip where I bought a dirt-cheap charger at a truck stop.
You're very welcome! ... and good luck with your project!
Thanks! That does make it clearer. I appreciate it.
Cable wattage and adapter wattage, MacBook Air M2 2022
