Apple have acknowledged that some USB C charge cables, packaged with MacBooks and sold as accessories throughout June 2015, may intermittently charge or complete fail to charge your devices. This is believed to be due to a failing in the manufacturing process.
Apple have now launched a replacement program for all cable owners effected by the failure.
The cables are clearly marked, and are easy to identify, check the image below for an example
The article published by Apple can be found here.