Using 12 V 2A supply unit for higher amp value
You can't create 12V 8A from a 12V 2A supply in any meaningfull way. Period. 

The supply won't (safely) provide more than 12 * 2 = 24 Watt, and you require 12 * 8 = 104 Watt. If you could do this you would have solved the world's energy problem.