Why is this Chinese cable slower when charging ?

[winlogon2]

Hi,

I bought 3 USB-microUSB cables from China, and all of them appear to be charging my HTC desire much slower than any other original cable.

It's not about the plug - I've done tests while charging from a PC.

What's going on inside the cable ? I thought it was just wires.. why would wires charge slower than others ?

Thanks

 

[winlogon2]

^