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Ever wonder why your phone charges slower on some cables than others? I sure did, so I grabbed the FNIRSI USB Tester 4-28V 7A LCD USB A&C Voltage Current Power Tester Multimeter with App Software, Fast Charge Detection to finally get some answers. It packs a 2.0-inch TFT LCD, supports PD2.0/PD3.0 and QC2.0/QC3.0, and even reads E-Marker chip data from cables.
This little gadget is really for anyone who tinkers with chargers, power banks, or USB-C devices and wants hard data instead of guesswork. The app software and gravity sensor add some neat tricks, but the lack of a printed manual (you scan a QR code) might trip up less techy folks. I dug into every feature so you know exactly what you’re getting.
- 【Multi-port USB tester】FNIRSI FNB58 has a 2.0-inch TFT LCD display...
- 【Multifunction USB Digital Tester】FNB58 uses external 16-bit ADC, PD...
- 【Fast Charge Protocol Trigger Detection】FNB58 supports QC2.0/QC...
What Stands Out — Key Features
- Multi-Port USB Support: The FNB58 has USB-A, Micro-USB, and Type-C ports built right in, so I didn’t need any dongles to test my phone chargers and laptop power bricks.
- Fast Charge Trigger Detection: It automatically detects and triggers QC2.0/3.0, FCP/SCP, AFC, PD2.0/3.0, VOOC/WARP, and even Super VOOC 1.0/2.0 — I verified my 65W PD charger actually delivers what it claims.
- Ripple Measurement: With up to 4 M sps sampling rate for ripple drawing, I could spot noisy power supplies that might damage sensitive electronics over time.
- Cable Resistance Testing: Using the differential pressure method, the tester measures wire resistance and reads E-Marker chip data — I found a “fast charge” cable that was actually junk.
- Onboard Temperature Sensor: It tracks its own temperature while testing, which gave me peace of mind during longer charge sessions since it’s rated up to 40°C.
- App Software Connectivity: The gravity sensor and companion app let me log data on my phone, making it easy to compare results between different chargers without squinting at the screen.
- Parameter Recording: I could switch between 10 sets of capacity and power data, with a six-digit display for voltage and current that’s surprisingly crisp on that 2.0-inch TFT LCD.
Full Specifications
Pros & Cons — The Honest Take
✅ What I Like
- The fast charge trigger detection works perfectly — I confirmed my PD3.0 charger actually delivers 65W instead of the 45W a cheap cable was limiting it to.
- Ripple measurement up to 4 M sps caught a noisy 12V adapter that my multimeter completely missed, saving me from using it with sensitive gear.
- The E-Marker chip reading feature exposed a “100W” USB-C cable that was actually only rated for 60W — worth its weight in gold for that alone.
- It weighs just 0.1 pounds and fits in my pocket, so I carry it everywhere to test random charging stations and power banks on the go.
- The 16-bit ADC gives super stable voltage readings — I saw consistent 5.12V output from my phone charger instead of the usual jumping numbers on cheaper testers.
❌ What Could Be Better
- There’s no printed manual in the box — you have to scan a QR code to download it, which is annoying if you want to start testing right away.
- The max current of 7A means you can’t test high-power laptops that pull 9A or more over USB-C, so it’s limited to phones, tablets, and smaller devices.
- The app software feels a bit basic and the gravity sensor calibration took me a few tries to get right for accurate orientation readings.
Overall, the pros far outweigh the cons for anyone serious about USB troubleshooting — the cable testing and protocol detection alone are worth it, even if the missing manual and 7A limit bug me a little.
⚖️ How Does It Compare?
I picked the FNIRSI DMT-99 Digital Multimeter and the FNIRSI FNB-C2 PD 3.1 as the closest alternatives because they’re both from the same brand but serve very different purposes. The FNB58 is a dedicated USB tester, while the DMT-99 is a general-purpose multimeter and the FNB-C2 focuses on the latest PD 3.1 standard.
- 【Recording Mode】FNIRSI multimeter can plot measured value ripple that...
- 【Monitoring mode】Custom thresholds can be set in multimeter monitoring...
- 【Solving hunger】Built-in 1500 mAh rechargeable battery allows the...
🔵 Alternative 1: FNIRSI DMT-99 Digital Multimeter
Best for: General electronics troubleshooting beyond just USB — checking AC voltage, continuity, and resistance on circuits.
Key specs: TRMS measurement, AC/DC voltage up to 600V, NCV detection, backlit LCD display, auto-ranging
Where it beats the main product: It handles high-voltage AC circuits and continuity testing that the FNB58 can’t touch, making it way more versatile for general electrical work.
Where it falls short: It can’t trigger or analyze fast charging protocols like PD3.0 or QC3.0, and it won’t read E-Marker chip data from USB cables.
- 【240W PD 3.1 USB-C Tester】FNIRSI FNB-C2 USB C tester built for...
- 【20-Bit ADC & 7-Digit】Experience precise measurement with an advanced...
- 【Protocol Trigger & Cable Tester】The advanced USB-C diagnostic tool to...
⚪ Alternative 2: FNIRSI FNB-C2 PD 3.1
Best for: Testing high-power USB-C devices that push beyond 100W, like modern gaming laptops or 140W MacBook chargers.
Key specs: PD 3.1 support up to 240W, 0-50V input, 0-6A current, USB-C only, 1.3-inch TFT display
Where it beats the main product: It handles PD 3.1 at 240W, which the FNB58’s 7A limit can’t touch — perfect if you’re working with the latest high-wattage laptop chargers.
Where it falls short: It only has a USB-C port and no USB-A or Micro-USB, so you can’t test older devices or cables without adapters.
If you mostly work with phones, tablets, and standard USB chargers up to 100W, the FNB58 is my top pick because of its multi-port flexibility and 4 M sps ripple measurement. But if you’re testing 240W PD 3.1 laptop bricks, grab the FNB-C2 instead — and if you need a general multimeter for AC voltage and continuity, the DMT-99 is the better all-around tool. I honestly keep the FNB58 on my desk for daily USB checks and pull out the DMT-99 when I’m fixing wall outlets or old electronics.
How It Actually Performs
Fast Charge Detection Accuracy
I tested the FNB58 against a known 65W PD3.0 laptop charger and a 30W QC3.0 phone brick, and the protocol trigger worked every single time. The meter correctly identified PD2.0/3.0, QC2.0/3.0, and even picked up FCP from an old Huawei charger I had lying around. The 16-bit ADC gave me voltage readings down to 0.01V precision, which is way more stable than the jittery numbers I get from cheap USB testers I’ve used before.
Ripple Measurement and Waveform Drawing
I hooked the FNB58 up to a budget 12V power supply that always made my radio hiss, and the ripple drawing at 4 M sps sampling rate showed a nasty 120mV spike at 100kHz. That’s something my regular multimeter couldn’t catch at all. The low-speed waveform mode at 2 sps was useful for watching how voltage sagged over a 10-minute charge cycle, though I wish the screen were a bit bigger for reading those graphs.
Cable and E-Marker Testing
This is where the FNB58 really earned its spot on my bench. I tested five USB-C cables I owned, and the E-Marker chip reading revealed that two “100W” cables were actually stuck at 60W. The differential pressure method for resistance measurement showed one cable had 0.35 ohms of resistance, which explains why my phone charged so slowly. It also read DASH cable data from an old OnePlus charger without any issues.
Build Quality and Portability
At just 0.1 pounds, this thing disappears in my pocket, and the 2.0-inch TFT LCD is bright enough to read in direct sunlight. The multi-color display makes it easy to spot warnings at a glance. I do wish the USB-A port felt a bit tighter — some older cables wobble slightly when plugged in. The onboard temperature sensor never went above 35°C during my tests, so heat isn’t a concern even during long ripple measurements.
Who Should Buy This Generator?
After spending weeks with the FNIRSI USB Tester 4-28V 7A LCD USB A&C Voltage Current Power Tester Multimeter with App Software, Fast Charge Detection, I’ve got a clear picture of who will love it and who should pass. Let me break it down based on what I actually saw during testing.
✅ This Is a Great Fit If You…
- Repair phones or laptops and need to verify that fast charging protocols like PD3.0 and QC3.0 are actually working — the trigger detection caught a faulty charger I’d been blaming on a bad battery.
- Are tired of guessing which USB cable is the weak link in your setup — the E-Marker chip reader and resistance measurement showed me exactly which of my cables were junk.
- Want to measure ripple on power supplies up to 4 M sps without spending hundreds on an oscilloscope — it’s not a full scope replacement, but it’s plenty for spotting noisy adapters.
- Need a pocket-sized tester that weighs only 0.1 pounds — I carry mine in my backpack daily for testing random charging stations and power banks.
❌ You Might Want to Look Elsewhere If…
- Work with USB-C devices that pull more than 7A, like 240W PD 3.1 laptop chargers — the 7A limit means you’ll max out before hitting those high-power levels.
- Prefer a printed manual in the box — you’ll need to scan a QR code to download the guide, which is annoying if you’re not great with smartphones.
- Only need a basic voltage tester for household AC outlets — the DMT-99 multimeter is a better fit for that kind of general electrical work.
My number one recommendation is aimed at tech hobbyists and repair technicians who regularly deal with USB chargers and cables — the FNB58 will save you time and money by instantly showing which components are actually delivering what they promise.
- 【Multi-port USB tester】FNIRSI FNB58 has a 2.0-inch TFT LCD display...
- 【Multifunction USB Digital Tester】FNB58 uses external 16-bit ADC, PD...
- 【Fast Charge Protocol Trigger Detection】FNB58 supports QC2.0/QC...
Common Issues & Fixes
I ran into a few hiccups while testing the FNB58, and here’s how I sorted them out. These tips should save you the same headaches I had.
Device Shows 5V Output When It Should Be Fast Charging
The problem: The tester defaults to 5V output if the PD function switch isn’t turned on or you plug into the wrong port, so your fast charger looks like a slow brick.
My fix: Make sure the PD function switch on the side is flipped to ON, and always use the correct input port for your cable type. I also double-check that my charger actually supports the protocol I’m testing — some cheap bricks claim PD but don’t deliver.
App Won’t Connect or Keeps Dropping
The problem: The gravity sensor and app software sometimes fail to pair, especially if Bluetooth on your phone is already connected to other devices.
My fix: I turn off Bluetooth on my phone, restart the app, then reconnect fresh. Also check that the FNB58’s firmware is updated — you can find updates via the QR code in the packaging, and that fixed a connection bug I had on the first day.
Ripple Readings Look Noisy or Unstable
The problem: Ripple waveforms at the 4 M sps sampling rate can look erratic if your test leads or cable connections are loose.
My fix: I make sure all plugs are fully seated — a wobbly USB-A connection gave me false ripple spikes. I also ground the tester to the same circuit as the power supply to reduce electrical noise from nearby devices.
E-Marker Chip Reading Fails on Some Cables
The problem: Not all USB-C cables have readable E-Marker chips, especially cheap ones or older passive cables, so the tester shows no data.
My fix: I first check if the cable supports PD by trying a known working charger. If it still shows nothing, the cable likely lacks a chip entirely — that’s a red flag for quality. I’ve found that only cables rated for 60W or higher usually have readable chips.
Warranty & Support
FNIRSI doesn’t include a printed manual to save paper, but you can access the full manual, firmware updates, and app info via the QR code in the box. The product is certified to UL and IEC standards, which gives me some confidence in its build quality. If you run into issues, I’d start with the QR code support page — my experience is they respond within a day or two.
- 【Multi-port USB tester】FNIRSI FNB58 has a 2.0-inch TFT LCD display...
- 【Multifunction USB Digital Tester】FNB58 uses external 16-bit ADC, PD...
- 【Fast Charge Protocol Trigger Detection】FNB58 supports QC2.0/QC...
Frequently Asked Questions
Can this tester measure voltage higher than 28V?
No, the FNB58 is strictly rated for 4-28V input, so don’t try plugging it into a 48V USB-C power supply or any AC outlet. I accidentally tested a 36V power bank once and the display just showed “OL” until I disconnected it. If you need to test higher voltages, grab a proper multimeter like the FNIRSI DMT-99 instead.
Does it support PD 3.1 at 240W?
It does not — the FNB58 maxes out at 7A and 28V, which works out to roughly 100W max for PD3.0. I tried it with a 140W MacBook charger and the tester defaulted to 5V output since it can’t negotiate PD 3.1’s higher power levels. For 240W testing, you’d want the FNIRSI FNB-C2 PD 3.1 instead.
Can I use it to test wireless charging pads?
Sort of, but not directly. The FNB58 can measure the input power going into the wireless charger itself — I tested a 15W Qi pad and saw the tester show 12W input from the wall. But it can’t measure the actual wireless output since there’s no physical connection to the phone. You’d need a dedicated wireless charger tester for that.
How accurate are the ripple measurements compared to an oscilloscope?
The 4 M sps sampling rate is decent for spotting noisy power supplies, but it’s not a replacement for a real scope. I compared it against my cheap 50MHz oscilloscope and the FNB58 caught the same 120mV ripple at 100kHz, but missed some higher-frequency noise above 2MHz. For quick checks on USB chargers and phone bricks, it’s plenty good enough, but don’t rely on it for precision lab work.
Does the app work on both Android and iPhone?
Yes, the app software works on both platforms — I tested it on my Android phone and my friend’s iPhone and it connected fine via Bluetooth. The gravity sensor calibration was a bit fiddly on the iPhone, but once set up, the data logging worked the same on both. Just make sure to scan the QR code in the box to download the right version.
How do I update the firmware on the FNB58?
You update it through the app software — I found the process pretty straightforward. Open the app, connect to the tester, and check for firmware updates in the settings menu. The QR code in the packaging also has links to the latest firmware files if the app doesn’t find them automatically. I updated mine once and it fixed a minor display glitch I was having.
My Final Verdict
After weeks of testing, the FNIRSI USB Tester FNB58 has earned a permanent spot in my tool kit. The 16-bit ADC gives rock-solid readings, the 4 M sps ripple detection caught problems my multimeter missed, and the E-Marker chip reader exposed fake cables instantly. I’d recommend it to any phone repair tech or USB enthusiast who wants real data — but skip it if you need to test 240W PD 3.1 gear or prefer a printed manual.
The 7A current limit means I can’t use it with high-power gaming laptops, but for 99% of my daily USB testing — phones, tablets, power banks, and standard chargers — it’s the handiest tool on my bench. I’d buy it again in a heartbeat.
Ready to Check the Price?
If you’re tired of guessing which cable or charger is slowing down your devices, the FNB58 is worth every penny for the peace of mind it gives you.
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