system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What makes a cable a 'fast charge' cable?

I have been seeing some 'fast charge' cables in shops and I was wondering how it basically worked.

I always thought a 5v 2a output would always output 5v 2a? Does the cable change this somehow?
gpt
Certain USB cables have specific resistance values between pins embedded into them to signal that they are suited for high-current charging. This in turn signals the phone it is allowed to draw higher currents from the wall plug (which has a similar mechanism).

The important thing to take away here is that the *phone* is in charge of what power is drawn, not the wall plug or the cable. The limit is purely for safety. Cheap cables might become a fire hazard at 2A or have too much loss. Cheap chargers might not be able to handle 2A and crash down in voltage / become hot / fire hazard.

It's quite easy to find a cheap Chinese cable that won't allow for fast charging, so "the cables do nothing" is demonstrably false.