Comment by ssl-3
3 days ago
Your Subaru+iPhone combo already tests that capability, does it not?
Just purge the known-bad cables already. :) (Gather them up and scrap them if the landfill seems like a harsh destination.)
In a situation of surplus, there's no reason I can think of where keeping charging-only cables around has merit.
Later on, if you need a cable that very specifically can do USB 3 speeds, then: Use a flashlight and look inside of the USB A connector. The ones that only have 1 row of 4 contacts will never be able to do USB 3, while the ones with 2 rows contacts will probably work fine.
I keep charge only cables for traveling. I don't trust the USB port in whatever I'm connecting to so the power only cable comes out.
I don't trust a random, in-the-wild USB port to provide sane power, so I bring my own charging stuff. :)
That said: My travel tends to happen with my own car, and that travel is never international. I can see how a charge-only cable would be beneficial for others.