USB Power Delivery is a standard published by the USB Implementers Forum, the organization that defines USB specifications. It governs one specific thing: how two devices connected by a USB-C cable agree on the voltage and current that will flow between them. Without it, a USB port delivers 5 volts and nothing else. With it, the same port can go up to 48 volts and 240 watts. The following explains the standard's power levels, its two power ranges, and the abbreviations found on a technical specification sheet.
What the standard adds to USB
The original USB specification sets its voltage. The port supplies 5 volts, the connected device adapts to it, and the available power is measured in a few watts. This works for a mouse or a storage drive, but not for a laptop.
Power Delivery replaces this fixed approach with negotiation. The source announces the voltage and current combinations it can provide. The powered device requests the one that suits it. The two devices agree, and the power exchange takes place at that value. If no combination is suitable, the connection remains at the original 5 volts: it does not fail, it simply charges at the minimum level.
This negotiation explains why two monitors that both carry the Power Delivery label do not always charge at the expected power level. The standard guarantees the negotiation protocol, not the value at which the agreement is reached.
The standard range, up to 100 watts
The first range defined by the standard is called the Standard Power Range, abbreviated SPR. It covers the most common values.
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Up to 2 amps at 5 volts.
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Then 3 amps or 5 amps, at 12 volts or 20 volts.
The ceiling for this range is 100 watts, reached with the combination of 20 volts and 5 amps. This is the level that covers the vast majority of laptops and desktop monitors. The 65 watts advertised by many monitors fall within this range.
The extended range, up to 240 watts
Revision 3.1 of the standard adds a second range, the Extended Power Range, abbreviated EPR. It introduces three additional voltage levels, along with the corresponding power outputs.
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28 volts, for 140 watts.
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36 volts, for 180 watts.
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48 volts, for 240 watts.
These values are intended for machines whose power consumption exceeds what a 100-watt charger can provide: mobile workstations, professional equipment, and devices equipped with a dedicated graphics card. A desktop monitor does not need this range to power an office laptop.
Fixed voltage or adjustable voltage
The levels described above are fixed voltages: the source offers them as they are, and the device selects one. The standard also provides for an adjustable voltage called AVS, for Adjustable Voltage Supply.
In this mode, the value is no longer selected from a list but adjusted continuously, from 15 to 48 volts, in 100-millivolt increments. The same mechanism goes down to 9 volts within the standard range. The benefit is that it matches the battery's actual requirements instead of rounding to the nearest available level, which limits the heat generated during charging.
The abbreviations found on a specification sheet
Four abbreviations commonly appear on technical specification sheets, and each indicates something different.
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PD indicates that the device can negotiate according to the standard. On its own, this abbreviation says nothing about the power level.
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SPR refers to the Standard Power Range, which stops at 100 watts.
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EPR refers to the Extended Power Range, which goes up to 240 watts.
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AVS refers to adjustable voltage in 100-millivolt increments.
A useful specification always combines the abbreviation with a wattage value. “PD” without a number leaves the power level unknown. On desktop monitors, the value is listed next to the port: the 27-inch 2560x1440 desktop monitor specifies its charging power on its product page, alongside its resolution. The complete range of monitors provides this information for each model.
The cable is part of the standard
The standard does not stop at the two devices: it also defines what the cable must be capable of carrying. A standard USB-C cable is designed for 3 amps. Beyond that, the standard requires an electronically marked cable, meaning a cable that contains a chip declaring its own capabilities and is rated for 5 amps.
This requirement determines access to higher power levels. The extended range, with its 140, 180 and 240 watts, is only available with this type of cable. An underspecified cable does not cause a failure: the negotiation falls back to a combination that the cable can safely carry, and charging simply takes longer.
This is why the power advertised by a device should never be considered on its own. It describes what the device can offer, while the actual result depends on all three links in the chain: the source, the cable and the powered device.
