I own this 5V 6A power supply:
And I bought this adaptor:
What looks like the same adaptor cable is also available on ebay.
The power supply plug has inner positive and out negative, but it doesn't specify polarity for the adaptor cable. Tested, it works. Open circuit voltage measured, 5.21V.
Will this solve the low-voltage problems with the Pi?
Only partly. The USB sockets are severely current constrained, that is the way they are designed. So even if you have a USB hard drive that is powered off a USB2 socket, that only applies to "normal" USB2, not the Pi. A pity.
Anyway, I am now using this power supply, to ensure the chips will always have the full voltage.
Comments:1TB drives work on Pi Posted on 30 Nov 2016, 19:18 by admin
Thanks to information supplied by pakt, I am now running a 1TB hard drive on my Pi3, powered from a USB2 socket: