How does the iPad not electrocute people without grounding?
simulate this circuit &ndash; Schematic created using CircuitLab

Here there is DC isolation and some CM ferrite chokes (lightning immunity and EMI reduction) not shown and many regulator details missing, but the main cause is ferrite transformer capacitance coupling  that induces a differential impedance coupling to hot that is high but low enough to conduct up to 250uA by Safety Stds.

In other words even if you were 0 Ohms to ground the current would be limited by Vin/ total series Capacitance in SMPS XFMR or Imax=250uA = Vin * ωC  

Can you calc. Cmax?