Q: USB-C Multiport Limiting Power from Reaching Macbook

Hi everyone,

I've been a Macbook owner (2016) for a few months now (1.3Ghz, El Capitan). Lately, I've been exploring different ways to minimize my electronics kit when traveling. One promising option is to charge the Macbook via a USB-A to USB-C cable (Benson Teung approved, of course). That way, I can ditch the separate charger for a Macbook and use a high quality USB-A wall charger, which I need to bring with me anyway for iPhone and iPad charging.

This idea works in theory. I use an i-Orange USB-A to USB-C cable with a wall charger that can output 2.4A at 5V (12 Watts). When I plug the USB-C end into my Macbook directly, I see that I'm pulling 12 watts into the Macbook (Using Coconut Battery app), which is sufficient to prevent my battery from dropping when in use, and for a slow, but sufficient, charge when the screen is off. This remains the case if I use some of the other ports in the wall charger to simultaneously charge iPhone and iPad at 2A x 5V. The wall charger is good for 40A.

The solution falters when I add a Multiport USB-C adapter in line. If I plug the i-Orange cable into the Apple Multiport Digital adapter and then the adapter into my Macbook, I'm only getting 2 watts! Mind you, this is with nothing plugged into the Multiport adapter (no HDMI output, and no USB-A device)--I'm simply using the adapter for power. At 2 watts, my solution doesn't work.

I've tried the same setup with a different USB-C adapter. SmartOmi makes an adapater that allows power pass through and gives the user 3 x USB-A ports. If I use this adapter (again, with no USB devices plugged in) the Macbook consistently gets 7 watts. Better, but still not enough. It's as if the Multiport USB-C adapters just have garbage conversion rates.

All of this got me interested, and I ran a couple more benchmarks with the official, Apple 29 Watt charger. With no multiport adapter, I'm seeing the full 29 watts going to the Macbook. With the SmartOmi MultiPort Adapter, 24 Watts get passed into the Macbook. With the Apple USB-C MultiPort adapter, 23 Watts are making it to Macbook.

Just the numbers:

12 Watt Charger

Direct to Macbook - 12 Watts to Macbook - 100% - 0 Watts less than max

Through Apple Multiport - 2 Watts to Macbook - 16.6% of Max - 10 Watts less than max

Through SmartOmi - 7 Watts to Macbook - 58.3% of Max - 5 Watts less than Max

29 Watt Charger

Direct to Macbook - 29 Watts to Macbook - 100% of Max - 0 Watts less than max

Through Apple Multiport - 23 Watts to Macbook - 79.3% of Max - 6 Watts less than Max

Through SmartOmi - 24 Watts to Macbook - 82.7% of Max - 5 Watts less than Max

I tossed a USB-A flash drive onto each Multiport adapter, and that didn't seem to affect the Wattage getting to the Macbook in any of the above scenarios.

Unfortunately, I don't have my Kill-A-Watt to test at the wall how the these setups are drawing juice. It may be that the Multiport adapters are constantly drawing additional energy (and substantial amounts, at that). Alternatively, they may simply be inefficient at getting power to the Macbook.

What started as a question has turned into more of an analysis, but I'm curious what others have seen and experienced in this regard. For the time being, I still plan to ditch the USB-C charger and travel with my 40 watt x 4 port wall charger. When I need to use a USB-A device (for data purposes) in conjunction with my Macbook, I'll put the Multiport adapter in line and take the power hit while that's needed. I'd prefer to be able to keep the Multiport adapter plugged in all of the time, but such is life.