Review on UM34C+LD25 USB 3.0 Multimeter Bluetooth Voltmeter Ammeter & USB Electronic Load Tester - Measure Voltage, Current, Battery Power, Capacity, Charger, Temperature with USB Load Meter Tester by Adam Gambel

In this era of USB-charged devices, knowing how to charge them is important. Current (as well as the total transmitted power). I use the LD25 to test the performance of the chargers I have. Especially useful for testing new USB chargers you just bought. I put the UM34C in the charger and then the LD25 in it. I can then vary the load and control the charge voltage and output current. All is well.