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CCReference Guide / Strong
USB PD is a conversation on the cable, not a wattage printed on a brick. The charger advertises voltage and current steps. The device requests a contract. The cable can silently cap the result. Above 100 watts you have left Standard Power Range.
The argumentUSB Power Delivery is a protocol. The source offers power data objects (fixed voltages, and in later revisions adjustable modes). The sink requests a contract. USB-IF's PD 3.1 revision, announced in 2021, raised the ceiling from 100 watts at 20 volts to 240 watts using new 28, 36, and 48 volt rails, with an adjustable voltage supply between 15 volts and the charger's maximum. None of that happens if the cable cannot carry the current or is not an EPR cable above 100 watts, or if the device never asks. A PD logo after USB-IF compliance testing is the closest thing to a guarantee. A number on a generic brick is an advertisement.
When a charger or cable says it supports USB Power Delivery, what is actually guaranteed, and what is still up to the device and the cable?
PD is a negotiated contract, not a promise that every USB-C port puts out 100 watts. The sink asks. The source may refuse or offer less.
Standard Power Range is 5, 9, 15, and 20 volts, up to 100 watts (20 volts at 5 amps). Extended Power Range adds 28, 36, and 48 volts for 140, 180, and 240 watts.
Cables are part of the contract. Unmarked cables typically stop at 3 amps (60 watts at 20 volts). Above 100 watts you need an EPR-capable cable, not a leftover phone cord.
USB-IF certification and the charger logo are interoperability tests. GaN, 'fast charge,' and a wattage on the case are not PD.
USB-C is a shape. USB Power Delivery is a language spoken on that shape. A charger that implements PD tells the device, over a configuration channel in the cable, which voltages and currents it can offer. The device answers with a request. If both sides agree, they have an explicit power contract. If they do not, you get a slow charge, a warning, or nothing. The wattage printed on the plastic is the manufacturer's hope about the best contract, not a law of physics that applies to every port at once.
USB-IF announced PD Revision 3.1 in 2021 specifically to push that best contract from 100 watts to 240 watts. That jump is not 'more of the same 20 volts.' It is a new voltage neighborhood called Extended Power Range. If you only remember one line from this page, remember the 100 watt border.
USB-IF USB Charger (USB Power Delivery) page; Texas Instruments SPR/EPR design note.
Advertises power data objects: which voltages, how many amps, whether EPR or PPS is available. A dual-port brick may advertise less on port 1 the moment port 2 is occupied.
Electronically marked cables tell both ends their current and voltage limits. A 3 A unmarked cable will not become a 5 A cable because you bought a 100 W charger. EPR above 100 W needs an EPR cable, not a leftover 60 W cord.
Requests a contract it is designed to accept. A phone that maxes out at 9 V will not draw 140 W from a 240 W charger. The unused headroom is not a defect.
This is why two USB-C chargers with the same printed wattage behave differently. One might offer only fixed 5/9/15/20 volt steps. Another might add PPS, which some phones use to run cooler, faster charge curves. A third might be EPR-capable for a 16-inch workstation and still charge a phone on a 5 volt fallback. PD's job is that negotiation. It is not a promise that every device gets the headline number.
USB-IF says companies that want the certified USB charger logos must pass compliance testing, land on the Integrators List, and hold a trademark license. That is the adult version of 'PD certified.' A lightning bolt icon from a phone maker's proprietary program can be faster on that maker's phones and irrelevant or slower on everything else. Those programs ride on top of, or beside, PD. They are not PD.
Safety is a separate stack. IEC 62368-1 and national listing marks (UL, ETL, and so on) are about fire and shock. PD compliance is about speaking the protocol. A beautiful GaN brick can do one and not the other. What GaN chargers actually improve is the semiconductor and the size of the magnetics, not the contract language on this page.
PD means source and sink agreed on a voltage and current. The printed wattage is the best case, often shared across ports.
100 W is the SPR ceiling. Above that you are in EPR, with new voltages and a pickier cable.
Look for USB-IF certification when you care about interoperability. Treat mystery bricks as mystery bricks.
No. A port can be USB-C and only offer 5 volts at a limited current, or an older charging spec. PD is extra silicon and firmware talking on the configuration channel.
Only up to what the phone requests. A 240 W EPR charger should still offer the low-voltage rails a phone uses. The extra 210 watts are for a different class of machine.
Multi-port chargers have a total budget. PD lets each sink ask. The source is allowed to offer less than the single-port headline when two sinks are present. That is the protocol working, not a broken brick.
Sources and further reading
USB-IF's PD overview: PD 3.1 enables up to 240W; previously limited to 100W at 20V with 5A cables. New 28V, 36V, 48V fixed voltages enable 140W, 180W, 240W. Adjustable voltage supply lets the device request intermediate voltages between 15V and the charger's maximum fixed voltage. Power direction is not fixed. Certified logos require compliance testing and a trademark license.
Engineering summary of SPR versus EPR: SPR up to 100W (20V, 5A); EPR to 240W (48V, 5A); 5A cable required above 60W; EPR cable required above 100W; AVS in 100 mV steps from 15V to 48V in EPR mode.
Continue reading
Start from the hungriest device's PD profile, then check whether the charger's single-port output and its shared multi-port budget both clear that number. Add a cable that is rated for the current. Do not shop by the number on the lid alone.
Technology / Personal Tech / 7 min
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