I have tried with two different power sources. 12v bench top supply and a fully charged 12volt Sealed Lead Acid battery 10Ah.
Both wired directly to regulator (one at a time).
I don’t have a picture but will explain…
Ground out of regulator connected directly to Ground pin on usb male header.
+5v wire connected in series through multimeter and then to +5v pin on male header.
Then another multimeter connected across the regulator.
I have tried another 5v source into the usb cable and connector, and do not see any voltage drop, ruling out the cable voltage loss etc.
I purposely used thick wires to overcome any voltage loss.
Another test was done using a large adjustable resistor load bank, so was able to load the regulator a step at a time and noticed the voltage decrease at around 200mA of load.
The Raspberry Pi 2 also displays an ‘under voltage warning’ on screen as well.