Rod Speed wrote, on Thu, 08 Jan 2015 10:05:41 +1100:

Too much voltage will destroy things.

And does when the electronics in the
socket fails and delivers full mains
voltage to the device plugged into USB.

But that can happen with ANY USB charger.

To be more specific on the question, since the spec on two ipads
would be to source about 2.1 Amps x 2 which is 4.2 Amps of current
(aka 21 Watts) of power, is there a MORE POWERFUL dual-USB wall
outlet receptacle than the best one I found, so far?

http://www.enerlites.com/61501-tr2usb.html