Dell USB-C to USB Cable

I recently bought a new XPS 9350 (laptop 2) which has USB-C ports.  The laptop shipped with a USB-C adaptor.

I already had an existing XPS 9350 (laptop 1) which was just over a year old and has a USB-C port as well as standard USB.   

I used the USB-C cable which shipped with laptop 2 to plug into laptop 1 to back up the data onto an external hard drive.  Within 5 minutes of each other, laptop 1 stopped working and my external hard drive corrupted.

I spoke to Dell and they were very good and agreed to repair laptop 1 under warranty as it was only just over a year old.  I got it back yesterday and they have replaced the motherboard.  I wasn't so lucky with my external hard drive - I have lost all the data and been quoted £350 to recover it

My question is, could it be that the adapter corrupted both products or is it just a horrible coincidence? 

I tried to speak to Dell about it, but I don't think they really understood what had happened.  I'm really nervous about continuing to use the adaptor since but I also don't want to buy a cheap alternative that might also cause damage.