Got an AmazonBasics USB-C cable for a new MBA

Tesserax wrote:

FWIW. I'm sure you are already aware that there is a difference between a USB port type and a USB standard. USB 2.0 (a standard), can support 5-20V @ 0.1-5A or 0.5-100W of power. Actually, this would be true for USB 1.0 thru 3.2. What is really different between standards is the supported data transfer rates.

A USB-C port follows the USB 3.1 standard ... but not always. The Amazon cable should be fine.

Yes. I've actually worked on USB at my job and know the issues with USB 2.0 and how it's been marketed over the years. And I even recall when companies would refer to "USB 2.0 Full Speed" even though that meant 12 Mbit/sec and not 480 Mbit/sec. I wasn't sure what voltage the MacBook Air needs or what the 30W power adapter supplies. I read the reviews by Amazon users and it's all over the map including some saying it's limited to 3A at 5V (i.e. 15W) while others say it maxes out at 60W. I don't have the cable yet, but I was thinking when it arrives (and my wife doesn't tell me to mind my own business) that I can check under System Report to see what power it's rated as providing with that combo.

As far as I know, even Apple's standard ($19) "USB-C charge cable" is rated for data transfer at 480 Mbit/sec, although also meant for full power transfer. I still use "USB 2.0" as the speed indicator, and that's how Amazon describes their cable's data transfer rate:

• • Up to 480 Mbps data transfer speed; power output up to 5V, 3 Amp
  • Certified by USB-IF to be compliant with USB 2.0; backed by an AmazonBasics 1-Year Limited Warranty

Tesserax wrote:

Turns out, to my surprise, that there are HDMI standards for cables as well. Doh! I replaced the cable I was using with a higher rated one, and voila, problem solved ... so you can never be too careful choosing cables.

I'm not 100% sure because I haven't worked with USB-C, but there might be some sort of "signaling" going on with USB-C cables to indicate their capabilities, or possibly even some sort of active mechanism. Back in the day of USB 1.1 to USB 2.0, the requirements for cables didn't actually chance, and any fully compliant USB 1.1 cable could transmit "Hi Speed" USB (480 Mbit/sec).

OK - I had a closer look at the requirements. Apparently in order to meet 3.1 requirements, there needs to be some sort of active electronics, similar to those in Lightning cables. Otherwise it will default to 2.0 speeds. Also - even basic cables are supposed to be able to handle at least 3A and 20V (60W) so I'm not sure exactly what it means when Amazon claims that it's 3A and 5V.

https://en.wikipedia.org/wiki/USB-C#Cables

All USB-C cables must be able to carry a minimum of 3 A current (at 20 V, 60 W) but can also carry high-power 5 A current (at 20 V, 100 W). USB-C to USB-C cables supporting 5A current must contain e-marker chips programmed to identify the cable and its current capabilities. USB Charging ports should also be clearly marked with capable power wattage.

Tesserax wrote:

You should find that USB-C "charging" cables are typically thicker to handle the potential voltage that will go across them. For example, the Apple 30W USB-C charger, that came with your wife's MBA, is rated at: 5V @ 3A, 9V @ 3A, 15V @ 2A, 20V @ 1.5A

Oh yes. I totally understand V = I x R and how that relates to voltage/power loss across an inadequately thin cable. And it has to be exponentially thicker when it's longer. I remember trying to use some USB extension cables which didn't work because the voltage drop was too much.