Yep. At the risk of making an analogy that won't pass muster with the actual Electrical Engineers that inhabit this forum, voltage is like (and sometimes is called) "electrical pressure", a measure of how much resistance a charge can overcome, while amperage is a measure, more or less, of how many electrons are available right now. If you don't have a high enough voltage to push electrons through the circuit, it doesn't really matter how many electrons you have available. So first you must have sufficient voltage - but NOT too much, as that can fry circuits (think of electricity flowing through the circuit with such force that it forges its own paths, rather than politely staying on the marked trails). The Raspberry Pi wants 5 Volts - much less than that and the circuitry won't work, much more and the circuitry will fry. Once you achieve the required 5V, then the issue becomes, are there enough electrons available to feed all of the circuitry? That's where amps come into play - the Pi itself will run with something much less than the 2A (2 amps) that is often recommended, but all the extra add-on bits take power too. And the newer Raspberry Pi's (the 2B and the 3) are more power-hungry than the earlier ones. They used to recommend 1A or 1.5A power supplies (actually, I think they started out with 0.7A aka 700mA). But now, take a Pi 2, add a WiFi dongle, and the touchscreen display, and you really want more like 2.5A to keep all the circuitry from starving.
My Pi 3 and 7" touchscreen display are connected by the two GPIO jumpers between their respective 5V and ground pins (with an official Pi 5V/2.5A power supply plugged into the display), one of the recommended hookup methods, but according to this article (
https://www.raspberrypi.org/blog/the-ea ... i-display/ ), one of the other recommended methods is to connect separate 5V supplies to the Raspberry Pi and the Touchscreen Display. One can also plug the display and Pi together with a MicroUSB-to-USB cable, but I've seen a number of reports of that resulting in the dreaded rainbow square, indicating undervoltage (presumably due to excessive resistance in the USB cable). Using the GPIO wires method, I see the little rainbow square flicker once or twice during boot, but it never appears during normal running. Pimoroni also offers a cable splitter, which attaches to the MicroUSB plug on the end of your normal power supply cable, providing two MicroUSB plugs, to plug into both the display and Pi, which is said to work well.
that has 2.5 A.
