Can I use the 87W brick with a 3A (3 amp) usb-c cable or does it have to be a 4A cable to charge the 15" Macbook Pro?

I don't think there are any 4A USB-C cables for sale, and I'm not sure they are even compliant the USB-PD specs. The list of USB-IF certified cables only lists 3A and 5A cables.

That being said, you should be able to use either a compliant 3A or 5A cable. But, if the 3A cable is truly compliant, the Mac will recognize that it is only capable of 3A, and will only be able to draw ~60W from this power brick.

60W won't be enough to charge the battery at full speed while also doing CPU intensive tasks, but it should be enough to run the computer entirely off wall power while doing fairly intensive tasks (I just encoded a video file, which used all the CPU power the MacBook Pro 15" could muster, and it drew ~60W). It should also be enough to do lightweight tasks like web browsing, email, listening to music, or watching a movie while still charging a discharged battery at close to full speed.

• Answered by Erik S from Seattle
• Oct 27, 2017
• Flag as inappropriate Answer 1