peterlite wrote:The USB standard for charging devices is slack compared to the accurate voltage required by the Pi...
This is very true, unfortunately. Phone/tablet charging is far less voltage sensitive than powering a computer. I have tested 5V/2.4A chargers that dropped down to 4.5V at only 1A load. 4.5V will still charge your phone fine, but it won't run a Pi.
That's not to say they are all bad. I own a few different phone chargers with good regulation that work great on the Pi. In fact, my Pi3 has been running off of a RAVPower RP-PC002W charger for several months now. It's rated 5V/2.4A but actually outputs 5.3V and will still be above 5.2V at 2A load. 5.3V is a little high as the max recommended is 5.25, but the micro USB cable connecting power to the Pi will drop the voltage a bit, so it should be fine (also, it's less than a 1% difference).
I also have a few chargers from Ventev that maintain good 5V regulation under load (I have both home/AC and car/DC chargers from Ventev).
The problem with using a phone/tablet charger is, you often don't know until you try.
Another component that's just as important as the power supply is the Micro USB cable connecting the power. Many are quite poor at delivering power due to thin wires and high internal resistance. I did a post a while back on some of the best cables I have used: viewtopic.php?f=63&t=165393
My mind is like a browser. 27 tabs are open, 9 aren't responding,
lots of pop-ups...and where is that annoying music coming from?