I have both the Pi 2 and (as of recently) Pi 3. I have a power supply unit (PSU) for both:
- One no-name PSU for the Pi 2 that came as a part of a starter kit
- One official PSU for the Pi 3 that came as a part of another starter kit
I have noticed that if I connect the official 7 inch display to the Pi 2 with the no-name PSU I often get the little rainbow square indicating that power is not enough. If I add LAN connection and my camera board (the official one, v2), the touch on the display stops working or acts all weird (probably due to lack of power). This makes me think that the no-name PSU is either faulty or just of very poor quality.
With my Pi 3 and the official PSU I have no such problem. As I see from the official docs the recommended PSU current capacity for the Pi 2 is 1.8A while for the Pi 3 it's 2.5A. So basically both have the same requirements when it comes to the voltage but different ones when it comes to the current.
Will it be okay to use the PSU for the Pi 3 with a Pi 2? I can't actually find any information on an official Pi 2 PSU.