Will mains kill me if I'm using an adapter?
As long as you are using an approved consumer power supply (such UL, TUV etc depending on your locale in the world) it is designed such you are not normally exposed to any hazards. This assumes you don't do anything foolish such open it's sealed enclosure or dunk it in water. 

So - no the 5V cord coming out of it should pose no risk to you. Voltages below 48V are not considered hazardous to humans.

But don't stick any wires into an AC wall outlet.