Why is there 130V between my laptop charger ground, and Raspberry Pi 5V Supply Ground?
The problem is most probably caused by "Y" filter capacitors between the P &amp; N mains lines and the ground line in one of the supplies. 

If the ground line is grounded no voltage occurs compared to mains ground. If the ground line is ungrounded it floats at half supply due to the capacitor voltage divider formed by the two Y caps. 

As the impedance is high the voltage you see when you measure it depends on the meter design and the value of the Y caps. eg a supply with 0.001 uF Y caps is more liable to be 'loaded' by a meter than one using 0.01 uF Y caps.

The impedance of this floating voltage is such that an unpleasant sharp feeling may be felt if the ungrounded ground is touched but the currents are well below those usually deemed dangerous. However, equipment can be damaged by exposure to this AC couple voltage.

A solution is usually to ensure that all "grounds" are grounded to a common ground. If this grounding occurs when an interdevice signal cable is plugged in it may cause damage as connection is made. Long ago I had a brand new printer destroyed in this way the first time it was plugged into a PC.