Sorry for answering an OLD question that has a good answer, but I have a good solution too. Great for anyone who's not afraid of a little DIY.
I have a stack of Raspberry Pi's here. All of them have more than enough power at all times.
Since I wasn't too happy about getting expensive USB cables, and I'm tired of cheap USB cables that under-perform, due to low cable cross-sections, that drops voltages, get hot and stop working, I made my own solution.
Another plus-side to my solution, is that I didn't have to get an 8-port 20A hub (8 x 2.5A) To make sure they have all the power they could possibly need.
They are all getting power from a 120w laptop PSU. This PSU delivers a bit more than 10A @ 19.5V regulated DC. This voltage is way too high, so I had to have some fun.
I hooked two cheap DC-DC converters up to the PSU. They take any DC voltage from 24 to 12, and the ones I got, outputs a nice ~5.1v under load.
- Link (Not this exact module, but similar)
From the outputs on the converters, I used the cheapest 18AWG(0.8mm²) cable I could find. 18 AWG is actually alot thicker than needed.
- Link (Looks like this. I got one red, and one black spool)
I also got a bunch of micro USB B plugs with solder tabs.
- Link (Could be these. Not sure)
On the plugs I used, I shorted the D+ to the D- line, since I don't know if the Raspberry checks what power supply it is connected to, and I soldered the 18 AWG cables to the VDC and GND pins. Then I put shrink tubing on the connectors to make it look a bit better.
I tested with dummy loads to see how the dc-dc converters held up.
- With a 20mA load each, they buth output 5.19V
- With a 10A load each, one were at 5.09V, and the other 5.1V
I ran the test for 30 minutes to see if voltages and temperatures were stable.
Now, I doubt that they will EVER draw that much power, but at least they have a good supply.
PS: The reason why I didn't power the 5v rails directly, is the protection offered by the polyfuses.
A tip: I put a 10.000mAh portable charger between the PSU and one RPi3 as a simple UPS too.