> Direct USB-C to USB-C extensions are explicitly forbidden for safety and performance reasons because they defeat built-in safety mechanisms.
> All USB-C to USB-C cables should support 60W charging, but there are also cables that support 100W and 240W. USB-C chargers and devices identify a cable's capabilities by reading what's known as an electronic marker (e-marker) inside the cable that explicitly reports >60W charging and/or 5Gbps or faster data transfer capabilities. A USB-C charger will first read a cable's e-marker and adjust its power output based on what the connected cable's maximum charging capacity is.
> The problem with extension cables in general is that they don't (and can't) have an e-marker, since by design, normal cables only have one addressable e-marker. Therefore, neither the device nor the charger is aware of the presence of an extension. If your USB-C to USB-C extension only supported 60W, and you connected it to a charger/device combo that could do 100W or more, you could start a fire. This failure is particularly insidious because it can potentially lull the user into a false sense of security; everything might work as expected until they change something, like upgrading the charger, and then it could fail catastrophically.
> Another reason extension cables don't work well is that the signal integrity requirements for USB-C's higher transmission rates are very strict. Believe me when I say that cable makers would make longer cables if they could.
Quoting OSTz on Reddit (https://www.reddit.com/r/UsbCHardware/comments/10xj74r/why_d...):
> Direct USB-C to USB-C extensions are explicitly forbidden for safety and performance reasons because they defeat built-in safety mechanisms.
> All USB-C to USB-C cables should support 60W charging, but there are also cables that support 100W and 240W. USB-C chargers and devices identify a cable's capabilities by reading what's known as an electronic marker (e-marker) inside the cable that explicitly reports >60W charging and/or 5Gbps or faster data transfer capabilities. A USB-C charger will first read a cable's e-marker and adjust its power output based on what the connected cable's maximum charging capacity is.
> The problem with extension cables in general is that they don't (and can't) have an e-marker, since by design, normal cables only have one addressable e-marker. Therefore, neither the device nor the charger is aware of the presence of an extension. If your USB-C to USB-C extension only supported 60W, and you connected it to a charger/device combo that could do 100W or more, you could start a fire. This failure is particularly insidious because it can potentially lull the user into a false sense of security; everything might work as expected until they change something, like upgrading the charger, and then it could fail catastrophically.
> Another reason extension cables don't work well is that the signal integrity requirements for USB-C's higher transmission rates are very strict. Believe me when I say that cable makers would make longer cables if they could.