AC to DC 12V 2A USB adapter
The cost of  Flash memory in $/MB has dropped rapidly with technology as they have squeezed more analog memory bits per cell and shrunk the cell size. 

What was once $50/GB not long ago, is now $50/TB and in some cases $12 for 2TB, more or less.  1TB=1000GB

So no need for a fast heavy HDD for backup unless you have other specs TBD.