How to test USB charger

Unboxing! This is so called Charger Doctor – a passthrough USB device, which you plug into a USB port, and connect other USB devices to it.
Click to buy.

Charger Doctor displays voltage and power consumption of the connected device. It is really cheap. With no downstream devices plugged in, Charger Doctor reads zero. I do not own RMS-enabled testing hardware, neither do I have any desire to nitpick accuracy of Charger Doctor measurements. I bought it as an easy way to detect serious malfunctions of USB chargers, like when voltage output drops from 5 to 1 under minor load. So the measurements do not have to be exact. So just to showcase how Charger Doctor works, I will connect it to a 2A power adapter and connect various USB devices through it. The first device is a USB powerbank for a single lithium-ion 18650 battery. The next one is a USB charger for 2 AA batteries. The readings are as follows, and the device label states this power requirements. An Android smartphone. And the tablet, from which this 2A charger comes from, refused to charge through Charger Doctor. This is probably due to USB standard requiring data pins to be shortened when drawing over 0.5 from a USB port, while Charger Doctor is a pass through device on all pins, data included. So the charge doesn’t happen, as the tablet controller blocks it. This theory is proved by this electronic cigarette device, which is too dumb to follow any standards, and just draws as much power as it wants.

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