ArduinoDroid with Arduino R3 interface problem

Hello Namste..
I am using Arduino R3 (original) tried to upload sketches from ArduinoDroid app. Using Moto G2 with Lolipop 5.0.2 Works perfectly started with Blink , changed delay and worked flawlessly..!
Only Problem is Arduino drains my battery rapidly.
So, Tried with external power supply 12V 1A adapter..
Here is a catch.. my mobile screen started behaving "ghostly" ! it shows Rapid touches speedy screen changes.. even when it was lying on table..!
When unplugged the external supply it worked as before..
Any idea.. what is wrong or am I barking the wrong tree??
Thanks in advance.