Why Is My USB-C Charger Not Fast Charging? Test with FNIRSI FNB58BT Malaysia
Why Is My USB-C Charger Not Fast Charging? Test with FNIRSI FNB58BT Malaysia
A USB-C charger may be rated at 20W, 45W, 65W or even higher, but that does not mean your phone, tablet or laptop will always charge at the maximum rated power.
If your device is charging slowly, the problem could come from the charger, USB-C cable, charging protocol or the device itself.
Instead of replacing components one by one, a USB tester such as the FNIRSI FNB58BT can help technicians investigate what is actually happening during charging.
Why Doesn't a 65W Charger Always Output 65W?
This is one of the most common misunderstandings about USB-C charging.
A charger marked 65W means that it is capable of providing up to its specified maximum output under suitable conditions.
It does not continuously push 65W into every connected device.
Actual charging power depends on several factors, including:
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Device charging requirements
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Supported charging protocol
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Charger output profiles
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USB-C cable capability
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Battery state of charge
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Battery temperature
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Device power-management system
For example, a smartphone connected to a 65W charger may only request 18W, 25W or another supported power level.
This can be completely normal.
Step 1: Check the Actual Voltage and Current
The first step is to measure what is actually happening.
Connect the FNIRSI FNB58BT between the charger and the device according to the appropriate test setup.
Observe the:
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Voltage
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Current
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Power
For example, if the tester shows approximately:
9V × 2A = 18W
then the device is receiving around 18W at that moment.
If you expected substantially higher charging power, further investigation may be necessary.
Step 2: Check the Fast-Charging Protocol
Modern fast charging depends on communication between the charger and connected device.
Common technologies can include:
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USB Power Delivery (PD)
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PPS
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Quick Charge
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Manufacturer-specific charging protocols
The charger and device need compatible charging capabilities.
A charger supporting one protocol does not automatically guarantee maximum charging speed with every smartphone.
The FNB58BT's protocol-related testing functions can help technicians understand what charging capabilities are available.
Step 3: Check the USB-C Cable
The cable is frequently overlooked.
You may have:
A good charger + a good phone + the wrong cable = slow charging.
Different USB-C cables can have different power capabilities and internal construction.
A poor or unsuitable cable may contribute to:
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Voltage drop
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Reduced charging current
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Charging instability
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Failure to reach the expected fast-charging mode
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Poor performance at higher power
When troubleshooting, try comparing the original cable with another known-good cable.
Keep the charger and device unchanged.
If charging behaviour changes significantly after replacing only the cable, the cable becomes an obvious area for further investigation.
Step 4: Check E-Marker Information Where Applicable
Some higher-power USB-C cables incorporate an E-Marker chip containing information related to the cable's capabilities.
The FNIRSI FNB58BT can be useful for compatible E-Marker testing.
This is particularly helpful when a technician has several USB-C cables that look almost identical externally.
You cannot reliably determine a cable's electrical capability just by looking at its connector.
Step 5: Don't Forget Battery Percentage
Charging power is not necessarily constant from 0% to 100%.
Many modern devices adjust charging power according to factors such as:
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Battery percentage
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Battery temperature
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Internal temperature
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Battery protection strategy
A phone may charge rapidly at a lower battery percentage and then gradually reduce charging power as the battery approaches full charge.
Therefore, a lower wattage reading does not automatically mean that the charger is defective.
Always consider the condition of the device during the test.
Step 6: Compare with a Known-Good Charger
Comparison testing is one of the easiest troubleshooting methods.
Suppose you have:
Charger A – suspected charger
Charger B – known-good charger
Use the same:
Device + cable + tester
and change only the charger.
Compare the voltage, current and power behaviour.
Then repeat the process while changing only the cable.
This method helps isolate individual components instead of changing several variables at once.
Example: 65W Charger but Only 10W Charging
Imagine a laptop or mobile device connected to a charger marked 65W.
The FNB58BT indicates approximately:
5V × 2A = 10W
Do not immediately conclude that the charger is faulty.
Possible reasons include:
1. The connected device does not request higher power
The device itself may limit charging.
2. The required charging protocol is not available
The charger and device may not have a compatible higher-power charging mode.
3. The cable is unsuitable
The cable may be limiting the charging system.
4. Battery management has reduced charging power
A nearly full or hot battery may charge more slowly.
5. The charger has multiple outputs
On some multi-port chargers, available power can change when several devices are connected.
Further testing is required before identifying the actual cause.
Can FNB58BT Tell You Whether a Charger Is Faulty?
It can provide useful diagnostic information, but the measurement must be interpreted correctly.
For example:
Low charging power does not automatically mean a bad charger.
The tester shows what is happening electrically.
The technician still needs to determine why it is happening.
This distinction is important.
The FNB58BT is therefore best treated as a USB charging diagnostic tool, rather than simply a device that gives a pass/fail result.
Useful Applications for Repair Shops
For mobile phone and electronics repair shops, the FNB58BT can be useful when customers report:
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Phone charging slowly
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Fast charging not working
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Charger compatibility problems
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USB-C cable problems
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Power bank charging issues
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Intermittent charging
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Unexpected charging wattage
Instead of immediately replacing the charger or cable, technicians can collect measurement data first.
This can make troubleshooting more systematic.
A Simple USB-C Troubleshooting Sequence
When fast charging does not work, follow a consistent sequence:
Measure → Check protocol → Check cable → Compare charger → Check device conditions
Avoid changing everything simultaneously.
Changing one variable at a time makes it easier to identify the source of the problem.
FNIRSI FNB58BT USB Tester Malaysia
The FNIRSI FNB58BT is suitable for users who need more than basic USB voltage and current measurement.
It can be considered for USB-C charger testing, fast-charging troubleshooting, power-bank testing, cable checking and electronics repair applications.
For FNIRSI FNB58BT enquiries in Malaysia, you may send us a photo of your charger, USB-C cable or device together with the charging problem.
MTM Precision Sdn Bhd
Showroom & Service Centre:
No. 29-1 & 29-2, Jalan Bandar 18,
Pusat Bandar Puchong,
47160 Puchong, Selangor, Malaysia.
Tel: 03-8080 7172
WhatsApp: +6016-660 7346
Email: mtmpre@yahoo.com
Website: www.mtmpre.com.my
Enquiries are welcome from Selangor, Kuala Lumpur, Johor, Penang, Melaka, Negeri Sembilan, Perak, Pahang, Kelantan, Terengganu, Kedah, Perlis, Sabah and Sarawak.
07 Oct 2026
