I have just ordered a pi 3 and a 5" backpack display with a few other things but I'm either supplying too much power or not enough the display draws 500mA through a micro USB cable I've plugged the damn thing into EVERY adapter in my house and used 4 different micro USB cables and no matter what the screen (with the hdmi cable connected to my pi) always shows white, black, pink, and yellow line things the display has only fully worked once and only very badly. So I was thinking would the USB ports on the pi supply enough power with an adjustable regulator attached? In short how much power will the USB ports supply?
P.S. There is no problem with the pi or display I know that much