I have a fairphone 3 which has a USB-C port for charging and the fairphone charger. I have found that the charge rate depends on which way round I plug in the charge lead.
One way it charges slowly, the other way round it charges rapidly.
Is this normal, a faulty cable, or a faulty phone?

 

If it's a proprietary charging cable it may not be fully symmetrical. What does the user manual say?

 

user manual??

 

Is this normal...?

No, it should not matter which orientation you use.

 

It is reversible. Possibly bad contacts on one side.

 

user manual??

Isn't one provided/available for the Fairphone?

 

It sounds like your cable is missing a pull down resistor. There are two lines, CC1 and CC2, that are used for PD negotiation, but only one is connected. So when the cable is reversed the proper one needs to be identified. It seems to be working then the right CC line happens to be connected but not negotiating the reverse situation.

 

If the cable follows spec it will be symmetrical. Just because it has a USB-C connector does not mean it meets spec. I have USB-C cables myself that are not symmetrical, they don't meet spec. It sounds like you have a non-spec cable, or a spec cable that is faulty.

 

Exactly as "Y" states! The resistor to communicate the charging mode is only present in one end of the cable, which may be only two conductors for power. So one way negotiates the higher charg, the opposite way only gets the "safe" charge rate.

 

Of course this isn't normal. Go buy a new charging cable and see what happens.