Is there an idevice app that tests the max amp output of a usb port?
We are using a MidContinent clock/usb and it says on the paperwork and the device '2.1amps' but it does not charge devices as fast as any other 2.1a supply I have.
You need two devices: a USB volt/ammeter and a resistor dummy load of 2.5 ohms. I have a reasonably good volt/ammeter bought on Amazon. My dummy load was a couple of bucks on eBay. You might also need a USB adapter or two between the big flat type "A" and the little flat "micro."
What you will find is that even if the power supply is good, the USB cable you are using might not be. Some are made with copper the size of angel hair which is fine for sending data but too resistive for carrying power.
First test: Plug the volt/ammeter into the power supply directly and measure the output voltage. It will probably be around 5 volts. Now plug the dummy load in and watch the voltage go down. A decent supply will still be above 4.6 volts. A good one above 4.8 volts. Note these readings.
Now put your cable between the power supply and the volt/ammeter and repeat the measurements. The loaded output voltage may go down as much as 0.4 volts more. If so, that cable goes into the garbage.
Good cables are available from monoprice.com. They are marked "28/24AWG" where the bigger 24AWG wire is used to carry the power. Good cables are also available from Anker via Amazon. They have a new line called "PowerLine." I have tested their previous line of large-wire cables and they were very good. I am sure this new line will be equally good.
Power supplies are a crapshoot. OEM power supplies marked "2 amps" are usually good. Aftermarket you have to test. Again, the Anker units I have tested have been good but I haven't tested all of their models.
The apps that show your device's power consumption are not totally useless but I have found that "Ampere" for Android does not correlate too well with the usb ammeter and, more importantly, the amount your device wants to draw depends on battery status. So unless the battery is close to flat, it may not be asking for the maximum from your power supply.
