Once upon a time there was only one way to charge a usb device and that was done at 5V and 500mA max, or so I've been told.
'Modern' USB Power Adapters like the Apple 1Amp, 2Amp and 2.4Amp and many Samsung chargers used for their tablets use a way of 'negotiating' higher power draws (anything above 500mA I presume) via Resistors or some other 'Smart' circuit on the D+ and D- (the data ports of the USB cable).
I have a couple of iPad chargers both the 10W (5V, 2Amp) and the 12W (5v, 2.4Amp) models and I tried to use them on the Raspberry Pi 2. I was surprised to notice that the Pi's red power LED was blinking all the time, plus the 'pulsing colored square in the top right of the screen' (apparently a newer firmware way to alert as to the insufficient current) was going on and off when I used the Pi 2 to compile something.
There is no question of faulty components, I have three Pi 2s exhibiting the same behavior on all my Apple chargers. My only conclusion it that the Pi can't use these 'smart' chargers and talk to them via the D+, D- data ports to 'negotiate' more power and is so kept on a short leash.
There is also this very good 3 USB port charger that IKEA has on sale (so new most websites don't have it) http://www.ikea.is/products/38976 that has a max of 2.4Amps on each port with a 3.4Amp total that also fails to work with the Pi 2 in exactly the same fashion.
Is this the case? Does the Pi need 'classic' (non-smart) power supplies to give it 'all they've got' without asking questions?
If so, is there a way to mod the Pi to tell these 'smart' chargers to give it more power? (heard something about shorting the D+, D- pin together on the Pi to achieve this or a 'smarter' solution of actually adding the right resistors to the ports to manually choose one of these 'smart'er modes.
PS. The internet is full of articles on how to mod a 'dumb' power supply for use in 'modern' devices, but none on how to use classic devices which need more power with 'modern' 'smart' chargers that behave in this way.