What Is a USB Tester? Types and Selection Criteria
A USB tester is a pocket-sized meter plugged between a charger and a device that shows the voltage, current and transferred capacity on the USB line.
A USB tester is a pocket-sized meter plugged between a charging adapter and the powered device that shows the voltage, current and transferred capacity on the USB line. It is used to see how much current an adapter, power bank, cable or computer port actually delivers and to tell whether fast charging has kicked in. A USB tester measures the power line; it is not a USB protocol analyser that decodes data packets.
Types of USB testers
- Type-A tester: A USB-A plug at one end and a USB-A socket at the other; measures adapters, power banks and computer ports.
- Dual-output (Type-A and Type-C) tester: Measures both port types in one housing; the Type-C side handles a higher current.
- Tester with electronic load: Draws current from the line with its own load, so you can check how much current an adapter or power bank can really supply without connecting a phone.
Measuring ranges in the UNI-T UT658 family in the catalogue vary by model:
| Model | Port | Voltage range | Current range |
|---|---|---|---|
| UT658 | Type-A | 3–9 V | 0–3 A |
| UT658B | Type-A | 3–9 V | 0–3.5 A |
| UT658A | Type-A | 4–24 V | 0.05–3 A |
| UT658DUAL | Type-A and Type-C | 4–24 V | Up to 3 A on Type-A, up to 5 A on Type-C |
Check the measuring ranges of the UT658C and the UT658LOAD with electronic load on their product pages.
Selection criteria
- Voltage range: In fast charging, the adapter rises above 5 V (9, 12, 15 or 20 V). The UT658 and UT658B, with a 9 V upper limit, are for 5 V and 9 V lines; to see 12–20 V fast charging, choose the UT658A or UT658DUAL with a 4–24 V range.
- Port type: To measure USB-C devices without an adapter cable, you need a model with a Type-C input.
- Current limit: The Type-A side measures up to 3 A and the Type-C side of the UT658DUAL up to 5 A; they are not suitable for lines drawing more current.
- Capacity and energy counter: The mAh and Wh counter totals what is transferred during charging; it is used to compare power bank capacity and charging time.
- Record memory: The UT658, UT658A, UT658B and UT658DUAL store 10 measurement records, which helps when comparing different adapters or cables in turn.
Common mistakes
- Exceeding the measuring range: At a voltage outside the range, the display shows an overload (OL) warning; do not use a 9 V-limited model on a 20 V fast-charging line.
- Overlooking the cable: The tester shows the value at the point where it is plugged in. To see the voltage drop along a cable, plug the tester in at the phone end of the cable.
- Not resetting the counter: The capacity counter adds to the previous reading; reset it before a new measurement.
- Mistaking it for a protocol analyser: A USB tester does not measure data transfer speed or data errors.
USB testers in the Welibaba catalogue
All 6 active products in the USB Testers category belong to the Unit UT658 family: UT658, UT658A, UT658B, UT658C, UT658DUAL and UT658LOAD. They are sold on a quotation basis. For measuring cells and batteries, see the Cell and Battery Testers category; for general electrical measurement, see Digital Multimeters.
Frequently asked questions
What does a USB tester measure?
It shows the voltage and current on the USB line in real time, and the capacity (mAh) and energy (Wh) transferred during charging as running totals.
How can I tell whether fast charging is working?
Plug the tester in between the adapter and the phone. When fast charging kicks in, the voltage rises from 5 V to 9 V or higher. To see values above 9 V, use a model with a 4–24 V range.
Can a USB tester measure power bank capacity?
Yes; discharge a fully charged power bank and read the total on the counter. The mAh value on the label refers to the internal cell voltage, so the mAh measured at the 5 V output comes out lower. Compare Wh values instead.
How do I get a price for a USB tester?
Products in this category are sold on a quotation basis. For price and delivery time, use the product advisor, WhatsApp or e-mail option on the product page.