Since the version 3.1 announcement on May 26, 2021, the USB PD standard has raised power delivery via USB-C ports from 100W to 240W, thanks to three new voltage levels: 28V, 36V, and 48V. This capability does not automatically apply to every laptop. A laptop only receives high wattage when the charger, the cable, and the internal power circuitry all support the same voltage level. This article explains the voltage negotiation mechanism, the requirements for enabling EPR charging mode, the role of 240W cables, and the limitations you should know before buying charging accessories for your laptop.
How Laptops and Chargers Negotiate Voltage via USB PD
Upon plugging in the cable, the USB-C port initially provides a default 5V. The laptop and the charger then exchange digital messages via the CC (Configuration Channel) wire within the cable. The charger sends a list of source capabilities (Source_Capabilities), detailing each voltage level alongside the maximum current it can provide. The laptop selects a compatible level and sends a request (Request). The charger accepts (Accept), switches to the new voltage, and signals it is ready (PS_RDY). This brief exchange is the essence of the USB PD protocol.
This principle explains why a high-wattage charger remains safe to use with older laptops. In USB PD, the power provider only announces its capabilities, while the power consumer decides the specific voltage and current it needs to draw. A laptop designed for 65W will request exactly that threshold, even if the charger is rated for 140W. Conversely, a laptop requiring 140W paired with a 65W charger will have to accept the lower level, resulting in slower charging or a "low power source" notification, depending on how the manufacturer designed the power management software.
Version 3.1 divides the power spectrum into two ranges. The standard SPR (Standard Power Range) maintains the 100W limit found in previous versions. The extended EPR (Extended Power Range) is the new addition, allowing power delivery to reach up to 240W. A laptop wanting to use EPR charging must first complete an SPR negotiation before requesting a switch to the higher range. The official USB Charger (USB Power Delivery) information page from the USB-IF confirms that 240W is achievable through fully featured USB-C cables and connectors.
Four SPR Voltage Levels and Three EPR Levels in PD 3.1
The SPR range includes four fixed voltage levels: 5V, 9V, 15V, and 20V. The first three typically pair with 3A current, corresponding to 15W, 27W, and 45W. The 20V level is where laptops draw most of their power, reaching 60W with standard cables and 100W when using an e-marker chip cable that allows 5A. The specification table for the 100W charger included with the Dell Pro Max 16 Premium MA16250 lists exactly these four levels: 5V/3A, 9V/3A, 15V/3A, and 20V/5A.
| Voltage Level | Range | Max Current | Max Power (W) |
|---|---|---|---|
| 5V | SPR | 3A | 15 |
| 9V | SPR | 3A | 27 |
| 15V | SPR | 3A | 45 |
| 20V | SPR | 5A (e-marker cable) | 100 |
| 28V | EPR | 5A | 140 |
| 36V | EPR | 5A | 180 |
| 48V | EPR | 5A | 240 |
The USB PD 3.1 update adds three fixed voltage levels - 28V, 36V, and 48V - which expand the thresholds to 140W, 180W, and 240W, respectively. All three levels maintain a maximum current of 5A, meaning the power increase comes from higher voltage rather than higher current. This approach keeps the wire cross-section in the cable at a reasonable size, since energy loss as heat in the conductor increases with the square of the current. Higher voltage, however, requires the components within a 240W cable to have better voltage tolerance.
From the table above, you can infer the limits of any given charger. A 140W charger does not have enough power for the 180W or 240W levels, so a laptop requiring more will only receive what the charger can provide. While a 240W charger is capable of all three new levels, the laptop will still only request exactly what its power circuitry can handle. When reading a USB PD charger label, you should look for the clearly printed voltage and current for each level rather than just looking at the total wattage on the front.
How the AVS Adjustable Voltage Range Benefits High-Power Laptops
In addition to fixed voltage steps, version 3.1 introduces AVS (Adjustable Voltage Supply) mode. According to a May 26, 2021, announcement from the USB Promoter Group, AVS allows a device to request any voltage within a range extending from 15V up to the highest fixed voltage supported by the charger, such as 28V, 36V, or 48V. With a 100mV adjustment step, a laptop can select a level very close to the actual requirements of the battery charging circuit rather than jumping between fixed steps.
The benefit lies in conversion efficiency. Inside a laptop, the charging circuit must step the input voltage up or down to a level suitable for the battery pack and the power rails for the processor. The smaller the gap between the input voltage and the required voltage, the less energy is converted into heat. Technical documentation from Texas Instruments describes how AVS helps fine-tune voltage within the 15V to 48V range to improve device performance and thermal efficiency.
AVS differs from the familiar PPS mode used on phones in two ways. According to analysis by Granite River Labs, PPS adjusts in 20mV steps and has current limits, whereas AVS uses 100mV steps and does not support current limiting. Therefore, you should not treat AVS and PPS as the same feature, even though both allow for flexible voltage changes. Whether a laptop that supports EPR charging utilizes AVS or only uses fixed steps can only be verified through the manufacturer's technical documentation.
EPR Charging Mode Only Activates When the Cable Confirms 50V Tolerance
With voltages reaching up to 48V, the new standard imposes strict requirements on cables. The USB Type-C 2.1 specification requires every EPR cable to have an e-marker containing EPR information, capable of operating at a rated 50V and 5A, and featuring a unique identification symbol specified by the USB-IF. Components on the cable's VBUS line are recommended to withstand at least 63V. This is why a 240W cable cannot be swapped for a standard phone charging cable, even if they use the same USB-C connector.
The transition to EPR follows a strict sequence. The laptop sends an EPR_Mode message with an Enter command, the charger confirms, and then it queries the cable's identity via a Discover Identity command. Only when the e-marker reports that the cable supports EPR does the charger send Enter Succeeded and announce voltage steps of 28V and above. If the cable is only a 100W type, the process stops and the laptop continues charging within the SPR range. To avoid this situation, you should purchase a 240W cable at the same time as the charger.
Once EPR charging mode is active, the laptop must periodically send an EPR_KeepAlive message to report that the connection remains stable. According to documentation from Plugable, if the charger does not receive this message within approximately 1 second, it will restart the connection and revert to SPR at 5V. This mechanism reduces the risk when a cable is loosened or unplugged mid-use at high voltage. The USB Promoter Group also emphasizes that safety requirements for 100W to 240W products are stricter than those for the low-power group.
Laptops Currently Receiving USB-C Charging Beyond 100W
To find out if a laptop supports EPR charging, you need to check the power section of the manufacturer's technical documentation. The Lenovo ThinkPad P1 Gen 8 (2025) is a clear example: PSREF documentation states the included charger is a 140W USB-C GaN that supports PD 3.1, and the Thunderbolt ports accept 140W input. Since 140W falls exactly on the 28V step, the laptop only receives full power when paired with a 240W cable. An older 100W cable will still charge the device but will stop at the SPR threshold.
| Laptop | Charger per manufacturer docs | USB-C Input | Highest voltage step |
|---|---|---|---|
| Lenovo ThinkPad P1 Gen 8 (2025) | 140W USB-C GaN, supports PD 3.1 | 140W | 28V (EPR) |
| Dell Pro Max 16 Premium MA16250 (2025) | 100W or 165W USB-C | 165W | 28V/5.893A |
| Dell XPS 16 9640 (2024) | 130W USB-C | 130W | 20V/6.5A |
| Lenovo ThinkPad P1 Gen 7 (2024) | 135W or 170W slim tip | 135W | Not listed in PSREF |
| Lenovo Legion 7 16IAX10 (2025) | 245W slim tip | 95W to 100W | 20V (SPR) |
The Dell Pro Max 16 Premium MA16250 (2025) offers two USB-C charger options. The 100W version only comes with integrated graphics, while the 165W version lists an additional 28V step with 5.893A alongside a 20V step with 6.5A. These two current levels are higher than the 5A standard, meaning a third-party USB PD charger that complies with the specification at the 28V step will only reach a maximum of 140W. You should stick with the included charger if you need full power for the discrete GPU.
The Dell XPS 16 9640 (2024) shows that a figure above 100W does not necessarily mean EPR charging. This laptop's 130W USB-C charger only has 5V, 9V, 15V, and 20V steps, with the 20V step providing up to 6.5A. Dell's spec sheet does not include a 28V step. If you are considering this model for graphics work, the article Dell XPS 16 9640 vs ThinkPad P14s Gen 6: Discrete RTX or long battery life for workstations? analyzes the relationship between discrete GPUs and battery life in more detail.
Why powerful gaming laptops still use barrel chargers
A 240W rating sounds high, but it is still lower than the requirements of many high-end gaming laptops. The Lenovo Legion 7 16IAX10 (2025) comes with a 245W slim tip charger, while its two USB-C ports only accept USB PD at 95W to 100W. Lenovo's PSREF also notes that the laptop supports a proprietary 140W protocol via USB-C, but only when using a specialized Lenovo charger. This means a standard EPR charger plugged into this Legion will only provide about 100W.
When USB PD power is lower than the rated capacity, the laptop will still operate but must balance its own power consumption. The PSREF for the ThinkPad P1 Gen 7 (2024) states that the Thunderbolt and USB-C ports accept 135W input; charging speeds and system performance may decrease if a lower-wattage charger is used, and a charger above 65W is recommended. For the Dell Pro Max 16 Premium, a charger under 100W will trigger a low-wattage adapter warning and slower charging speeds.
A practical approach is to keep the original charger at your desk and carry a more compact USB PD charger when traveling, accepting slower charging while handling light tasks. If you are choosing a workstation for design software, the article Laptops for CAD and simulation engineers - 5 workstations worth buying can help you finalize your configuration before you consider charging accessories. Power banks only provide high wattage if the output port specifications explicitly state 28V or higher.
Frequently Asked Questions (FAQ)
How much power will a laptop receive if an old 100W cable is plugged into a 240W charger?
Because a 100W cable lacks EPR information in its e-marker, the charger will not switch to EPR charging. The laptop will still receive a maximum of 100W at 20V/5A, which is sufficient for laptops with original chargers of 100W or less. To get 140W or more, you need to switch to a certified 240W cable.
Is it safe to plug a 65W laptop into a 240W charger?
Yes. Under the USB PD mechanism, the laptop only requests the voltage and current that its power circuitry accepts; the charger does not unilaterally push high voltage. The 28V to 48V range only appears when the laptop actively requests EPR and the 240W cable confirms it meets the standard.
What does the 240W logo on the cable jacket mean?
In September 2021, the USB-IF introduced power certification logos for USB-C cables at two levels: 60W and 240W. A 240W cable logo indicates the product has been tested by the USB-IF according to the USB PD 3.1 specification. You should prioritize cables with this logo rather than relying solely on promotional text on the packaging.
Can a USB PD power bank charge a 140W laptop?
Only if the power bank's output port supports EPR charging at 28V and you use a 240W cable. If the output port is rated for a maximum of 20V, the laptop will receive no more than 100W and may charge slowly during heavy workloads.
