text: Q:
  
  Car adapters (12V -> 5V) in parallel
  
  Am wondering if there are any risks involved in putting two (5V) car cigarette lighter adapters in parallel. They will be part of a setup replacing the car stereo, so will be connected to the "ignition" wire, not the cigarette lighter.
  The two adapters I have are very different in appearence, and one of them is rated 1.5A, the other one unknown. I need something like 2.5-3A.
  I assume both of them contain surge protection, which is one reason for using them.
  Any reason for not two in parallel?
  Clarification: parallel as in output sides connected.
  
  A:
  
  It depends. If the adapters are powering separate circuits, it should be fine, provided you're not exceeding the current rating of the wires. 
  However, connecting the outputs in parallel would not be a good idea, as any voltage difference in their outputs will place more of a load on one, possibly exceeding its rated current. You almost certainly will not be able to safely produce the sum of the two adapters' currents, as the weaker one will likely drop its output voltage, leaving the other adapter with most of the load. In this case, you're much better off buying a single large supply that can handle the current you need.
  
  