I bought this for developing my apartment emergency power system. The voltage and current readings were compared to a certified and calibrated fluke meter, and was roughly 1 to 2 percent off. Great accuracy.This handled the full 18 watts for Quick Charge 3.0 effortlessly.If you are a tinkerer working with USB power, this would be a great addition to the bench.

tells you what you want to know, good and inexpensive.

This compact tool has proven to be indispensable in my arsenal of repair equipment. It's incredibly useful for quickly identifying whether a device is receiving power properly, which saves me a ton of time and frustration. I appreciate its ability to eliminate guesswork by instantly indicating whether there's an issue or not, because I can't stand fumbling around with multiple cables, trying to diagnose a USB problem.However, there is one aspect where it falls short, data passthrough. Not being able to monitor the voltage and amperage while USB devices are in use can be somewhat limiting if want to keep track of fluctuations during use. Nonetheless, considering its affordability and ease of use, this USB Voltmeter remains a fantastic addition to my toolkit.

This product bill received very late and non-mention replacement and not update Amazon return policy I am not satisfy wastage of money

El voltaje que marca es aproximadamente 0.5 volts menor al real. Pero nada más. Todo funciona bien.

Worked for one session then it quit working.

does what it say.

Works as advertised and has a much broader measurement range than others I have looked at, bonus feature it can plugged in in either orientation

The Good:Very useful for testing real-time Voltage, current, capacity, charging temperature while a device is charging. Also to check if a battery pack can deliver its advertised capacity.If unplugged it keeps memory from last usage. While on, it can be deleted by pressing the button twice.It supports devices with QC2.0, QC3.0, BC1.2 (Battery Charging revision 1.2) & Apple voltage range.You could switch to three different display screens by just pressing the only button on this USB Digital Power Meter Tester.It appears to be very accurate.The Bad:No manual. I spent some time tinkering with it to find out all the info available here.I wouldn't know if there are other hidden settings.More Info:It is quite amazing what you can accomplish on this device with just one button.-Pressing the button once takes you to the next screen-Pressing the button once and holding until it beeps resets all-Pressing the button twice resets the capacity (Cap:)-Pressing the button three times resets energy (Ene:)-Pressing the button four times resets time (Time:)-Pressing the button five times, toggle the setting next to time: Off/AO/Manual-Pressing the button six times changes language from Chinese to English.The setting next to time on the second screen has three modes:-Off [device will be running non stop]-Automatic Off (AO..) [device will power off after it detects power draw stops].-Manual [device will power off after specified time].Automatic Off (AO..) and Manualare very useful if you don't want a device to keep drawing a little bit of current here and there after fully charged. Especially if you want to extend the live of your device Lithium-ion or to stop draining a battery pack.To set it to 'AO..' (from 'OFF') press button five times 'AO..' will blink then wait for device to beep.To set it manually to a specific time (from 1-24 hours), press button five times 'AO..' will blink, press one more time '24' blinks. Pressing button once will decrease the time by 1 hour (24, 23, 22, 21, etc) but if you press twice it will increase (21, 22, 23, etc). Since there is only one button you will have to go back to '24' to be able to select 'AO..' or 'OFF' again.Below, the data that could be displayed on each of the 3 screens.The 1st screen has 6 entries.Left (from top)-Voltage-Amps-Running timeRight (from top)-Watts-Amp Hours-Watt HoursThe 2nd screen has 8 entriesLeft (from top)-Negative pin (V-)-Positive data pin (D+)-Negative data pin (D-)-Positive pin(V+)Right (from top)-Resistance (O)-Temperature (°C)-Time-AmpsThe 3rd screen has 4 entriesFrom top-Voltage (V) / Current (A)-Capacity (Cap)-Energy (Ene)-Time (00:00:00) / Automatic Off (AO..)

(Gleaned from various postings and youtube videos.)The Eversame USB Digital Power Meter aka Juwei USB Safety Tester Model J7-tSpecifications • Input Voltage: 3V - 30V • Input Current: 0 - 5.1A • Accuracy: +/- 1%Accuracy compared to calibrated Fluke 87-5 Multimeter my J7-t reads 5.12V; my Fluke reads 5.137VSearch on the web for "USBmeter safety tester J7-t UK", which will bring you to a page with extensive testing of the J7-t and a view of its components.The J7-t has two USB type A connectors. The male connector is reversible so you can plug it into the power source either side up. The connector has a set of pins on each side of a thin blade that makes this possible. It won't withstand rough treatment.The female socket on the other end of the J7-t will accept a cable from the device to be charged as long as it's terminated with a Type A male connector.The J7-t displays one of three screens when plugged into a power source. The screen will be whichever last showed, but fresh out of the box, you should see Screen 1.Screen 1 ◦ voltage ◦ current ◦ watts ◦ elapsed charging time ◦ amp hours (cumulative) ◦ watt hours (cumulative)[If you have mistakenly held down the button (marked KEY) on the top edge of the J7-t while plugging it into the power source, you will enter calibration mode and see a different screen. Unplug the J7-t and try again.]The cumulative counter values are derived from the time a device has actually been charging through the J7-t. The count stops whenever charging stops and resumes when charging resumes. If the J7-t is unplugged from its power source, values are preserved and can be read when powered again. To clear the cumulative counters, hold the KEY button down until you get a beep.A short press on the KEY button will cycle the J7-t display through three screens. The remaining two are:Screen 2 ◦ voltage of all 4 pins (v-, d+, d-, v+) ◦ resistance of the connected load ◦ timer / temperature of the J7-t ◦ elapsed charging time ◦ currentScreen 3 ◦ voltage / current ◦ capacity / adjustment factor ◦ energy in watt hours / temperature of J7-t in °C ◦ elapsed charging time / timerKey PressesA quick press of the KEY button will do the following: • press 1 time to cycle through the three display screens when on Screen 3 • press 2 times to reset Cap: mAh • press 3 times to reset Ene: Wh • press 4 times to reset Time • press 5 times to set the charge timer • press 6 times to change language (English or Chinese)(Holding the KEY button down until you get a beep will clear all counters at once.)Charge TimerThe J7-t can be set to stop charging after a certain time, from 1 to 24 hours. By default the timer is off and shows on screens two and three as OFF. To set the timer, do five quick presses of the KEY button while on screen three. OFF will start flashing on the bottom of the screen. Continue pressing the KEY button until you reach the desired setting (AO is auto-off). After charging for the set time, the J7-t will stop charging, beep a few times, and display OFF on its screen. Pressing the KEY button brings the normal display back up.Calibration ModeTo enter calibration mode, hold the KEY button down when you connect the J7-t to its power source. Afterwards, a single press of the KEY button will cycle through the configurable settings, showing each setting alone on its own screen. • 0.00A a 2 amp source is required to calibrate amps • 5.12V a 5 volt source is required to calibrate volts • >30.0V set overvoltage cutoff • • >5.00A set overcurrent cutoff • X1.00 set mAh and wH adjustment factor (0.50 to 1.50)Double click the KEY button to change a value. When changing, a single click decreases the value; a double click increases the value. After a single or double click, immediately pressing and holding the KEY button will rapidly change values.The last screen in calibration mode shows a telephone number and website for Juwei, which is a creature of Shenzhen Ouju Technology Co., Ltd.To exit calibration mode, disconnect power to the J7-t.