Resistor style stripes on cables would be fun, a stripe for each feature such as bandwidth, power, etc; perhaps already suggested (and ignored). Though complement for ports would be trickier.
Embossing symbols in the style of thunderbolt might be the way to go, even if the standard is not fully adopted.
Honestly that's about all you need.
Even just a bandwidth indicator would be suitable 90% of the time.
My first attempt was different colors for each device, but was too tedious.
Three categories - low power, high power slow USB2, and 100W Thunderbolt.
- Low power: generic cables from wherever
- High power slow: cables that came with reputable charger (the vendor's cable, like Apple or Samsung; my favorite 3rd party charger is https://www.ravpower.com/products/rp-pc112-gan-tech-61w-wall...)
- Thuderbolt: I buy from https://eshop.macsales.com/shop/Thunderbolt