Multi-port Charger Power Fraud: Total Output 150W ≠ Simultaneous Charging of Three Ports

In daily use of multi-port chargers, many people encounter the problem that “the nominal total output is 150W, but charging 3 devices at the same time results in slowdown” — laptops charge slower and mobile phones fail to fast charge. The root cause lies in the opaque power distribution mechanism. The following disassembles from four aspects: technology, actual measurement, solutions and global specifications.

1.Dynamic Allocation Black Box: Single Port Full Load, Secondary Ports Hide “Power Stealing and Reduction”

The “total output power” of a multi-port charger is not the sum of the power of each interface, but relies on dynamic allocation technology. When a single port is fully loaded, other interfaces will implicitly “steal and reduce power”, forming a “black box effect” that is difficult for users to perceive.

• Technical principle: The internal power distribution chip adjusts the output according to the load. If a single port is connected to a high-power device such as a 65W laptop, the chip prioritizes this port and reduces the power of other ports to prevent overload. However, most brands do not mark the “dynamic allocation rules” and only promote the “total output XXW”, misleading users to think that each port can run at full speed at the same time.
• Actual scenario: Using a nominal 120W three-port charger, when charging a 65W laptop alone, the actual measurement is 63.2W (close to the nominal value); if a 20W mobile phone is added for charging, the power of the laptop drops sharply to 38.5W, and the mobile phone only gets 15.3W (not reaching fast charging). The total power of the two is only 53.8W, which is far lower than the nominal 120W.
• Key data: Industry tests show that for mainstream multi-port chargers with a total output of 100-200W, when “single port full load + 1 secondary port load”, the power of the secondary port is reduced by an average of 40%-60%; some low-end models have a reduction of up to 70%. For example, the nominal 18W mobile phone port actually outputs only 5-6W.

2. Actual Measurement Exposure: When Four Ports Are Used Simultaneously, the Total Power Shrinkage Rate Exceeds 30% at Most

To verify the authenticity of the “total output power”, three types of nominal 150W four-port chargers were selected for testing in a unified scenario (simultaneously charging a 65W laptop, a 20W mobile phone, an 18W tablet, and 5W wireless headphones). The results show significant differences in shrinkage:

• Type 1: The measured total power is 112.3W, with a shrinkage rate of 25.1%; the laptop port drops from 65W to 42.5W, and the tablet port drops from 18W to 12.8W, both of which are difficult to reach full speed.
• Type 2: The measured total power is only 104.7W, with a shrinkage rate of 30.2%; the mobile phone port is only 10.2W (far lower than the 20W fast charge), and the headphone port drops to 2.1W (less than half of the nominal 5W), resulting in a significant reduction in basic charging efficiency.
• Type 3 (independent power distribution): The measured total power is 141.5W, with a shrinkage rate of only 5.7%; each port is close to the nominal value (laptop 63.8W, mobile phone 19.2W, tablet 17.5W, headphone 5W), and the stability is better than the first two types.
• Conclusion: The power distribution design determines the output stability — most products with basic schemes have a shrinkage rate of more than 20% when four ports are used simultaneously; only products with independent distribution schemes can approach the nominal total output and meet the full-speed charging of multiple devices.

3. User Countermeasure: USB PD Decoy, Locking the Full-speed Charging of Laptops

In view of the slow charging of laptops caused by dynamic allocation, users can use a USB PD decoy (referred to as PD decoy) to actively lock the power to ensure the efficiency of high-priority devices.

• Working principle: Simulate the PD protocol of devices such as laptops, send a “fixed power demand signal” (such as 65W, 100W) to the charger, and force the charger to supply sufficient power to the target port, which is not affected by the load of other ports.
• Actual measurement effect: Using a nominal 150W basic charger, when the decoy is not connected, when the laptop and mobile phone are charged at the same time, the laptop only has 38.5W, and it takes 2 hours and 40 minutes to fully charge; after connecting the decoy to lock 65W, the laptop is stable at 63.2W, and the full charge time is reduced to 1 hour and 25 minutes. Although the mobile phone port drops to 12.8W, it does not affect basic charging.
• Purchase suggestions: High-quality PD decoys need to meet — Type-C gold-plated interface (reducing resistance and heat generation), support PD3.0/QC4.0 protocols (adapting to MacBook, Dell XPS, etc.), and have built-in overvoltage/overcurrent protection (complying with IEC 62368-1 standard) to prevent device damage.

4. Progress of Global Specifications: USB-IF Revises Labeling Rules to End “Vague Publicity”

In response to the confusion in power labeling, the global USB standardization organization (USB-IF) revised the “USB PD Multi-port Device Specification” in Q4 2024, requiring brands to mark both “total output power + interface combination power” to eliminate the misleading of only marking “total power”.

• Core revisions:

◦ Mark “maximum total output power” (such as 150W), and supplement “interface combination power”, for example: “150W (single port max 65W; dual ports: 65W + 30W; four ports: 45W + 20W + 15W + 10W)”;

◦ Prohibit vague expressions such as “total power XXW, each port can be fully charged at the same time”, and “dynamic allocation” must be noted;

◦ Attach a “power distribution diagram” to the packaging and instruction manual to allow users to intuitively understand the actual output.

• Industry impact: In August 2025, leading brands such as Apple, Anker, and Belkin have implemented the new standards. For example, Anker 737 (nominal 120W) is marked as “single port 65W, dual ports 65W + 30W, three ports 45W + 30W + 20W”; however, some small and medium-sized brands in Southeast Asia and Latin America still sell “old standard products”, so it is necessary to check the labels when purchasing.
• Comparison before and after: Before the revision, a 150W three-port charger only marked “total output 150W”, which easily made users mistakenly think that “three ports can be fully charged at the same time (such as 65W + 65W + 20W)”; after the revision, it is required to mark “total output 150W (single port max 65W, dual ports 65W + 30W, three ports 45W + 30W + 20W)”, making the information more transparent.