Will It Work? · Guide

Why a big charger can still charge your phone slowly

By Bulan Sarkar, founder of ElectronicsInfoline (since 2000)

A bigger charger does not make a phone or laptop charge faster by itself. Three things each cap the power, and the lowest one wins. Below are the three limits and five common setups, each worked through by the same tested logic as the checker.

Charging power is the lowest of three limits: the best profile the charger offers, what the cable can carry (3 A on a standard cable, 5 A on an e-marked one), and the maximum the device's maker gives. A 65 W charger on a 60 W cable gives a 65 W laptop 60 W; it gives a 25 W phone 25 W.

The three limits

Charger: its label lines. The total on the front is the most it gives; each line is a voltage at a current.
Cable: 3 A standard, up to 5 A when e-marked (USB-IF).
Device: the maximum its maker states, and the protocol it uses (plain PD, PD with PPS, or neither).

Figure 1. Charger 65 W, cable 60 W, laptop 65 W: the cable is the lowest, so the laptop gets 60 W.

Five cases, worked through

Example labels: 65 W charger 5V⎓3A 9V⎓3A 15V⎓3A 20V⎓3.25A; 30 W charger 5V⎓3A 9V⎓3A 15V⎓2A 20V⎓1.5A. These are inputs, as you would type them in the checker.

Cable limit

A 65 W laptop on the 65 W charger with a 60 W cable

60 W. Falls back to 60 W of the device's 65 W: the cable carries at most 3 A.

Device limit

A phone whose maker gives 25 W, on the 65 W charger

25 W. Fast-charges at up to 25 W, the device's full rate.

Charger limit

A 45 W tablet on a 30 W charger

30 W. Falls back to 30 W of the device's 45 W: the charger's profiles top out there.

No PPS

A PPS phone (45 W with PPS, maker states no other figure) on the 65 W charger without PPS

not stated. Charges on ordinary PD, not at full speed: the device needs PPS for its 45 W and this charger has none. The maker does not state the rate on ordinary PD, so we can't give a number; the charger can offer up to 65 W.

No PD

A device without USB PD on the 65 W charger

15 W. Falls back to 5 V: at most 15 W of the 18 W the device can take. The device does not use USB PD.

Figure 2. The 25 W phone on the 65 W charger: the phone is the lowest limit, and a bigger charger changes nothing.

Figure 3. USB-IF figures: a 60 W cable is tested at 20 V, 3 A; a 240 W cable at 48 V, 5 A. Any cable rated above 3 A carries an e-marker chip that tells the charger what it can take.

Tips and tricks

Change the cheapest part first. If the checker says the cable is the limit, a 5 A cable fixes it for far less than a new charger.
Before buying a bigger charger, find the device’s own maximum. Above it, extra watts go unused.
A charger with no PD at all leaves a USB-C device at 5 V: 15 W at most, whatever the box says.
On a shared multi-port charger, unplug the other device and try again before blaming the cable.

What we would do

Write down three numbers: the device maker's maximum, the charger's label lines and the cable's rating. Put them into the checker. Whichever part it names as the limit is the one to change, and only if the device's own maximum is higher than what you get now.

Questions people ask

Why does my phone charge slowly on my laptop charger? The phone takes no more than its own maximum, whatever the charger offers. If it needs PPS for its top speed and the laptop charger has none, it charges on the fixed profiles, which can be slower.

Can a cable really slow charging down? Yes. A standard USB-C cable is rated 3 A. At 20 V that is 60 W, so a 65 W or 100 W charger stops at 60 W on it.

What is the most a USB-C charger gives without USB PD? Without PD, USB-C runs at 5 V and the charger can advertise 1.5 A or 3.0 A, so 15 W at most.

Sources

Each figure on this page is quoted from the source below or worked out from them. Sources checked 20 October 2026, each quote read again against the source in a second pass.

USB-IF, USB Type-C Cable and Connector Specification, Release 2.0 (August 2019): The USB Type-C receptacle is specified for current capability of 5 A whereas standard USB Type-C cable assemblies are rated for 3 A. [...] Also, USB Type-C cable assemblies designed for USB PD and appropriately identified via electronic marking are allowed to support up to 5 A. usb.org/sites/default/files/USB%20Type-C%20Spec%20R2.0%20-%2…
USB-IF, USB Type-C Cable and Connector Specification, Release 2.0 (August 2019): All cables that are either full-featured and/or are rated at more than 3 A current are Electronically Marked Cables. usb.org/sites/default/files/USB%20Type-C%20Spec%20R2.0%20-%2…
USB-IF, USB Charger (USB Power Delivery) | USB-IF: Announced in 2021, the USB PD Revision 3.1 specification is a major update to enable delivering up to 240W of power over full featured USB Type-C® cable and connector. Prior to this update, USB PD was limited to 100W using a solution based on 20V using USB Type-C cables rated at 5A. usb.org/usb-charger-pd
USB-IF, USB-IF Introduces Fast Charging to Expand its Certified USB Charger Initiative (press release, January 8, 2018): Certified USB Fast Chargers support the Programmable Power Supply (PPS) feature of the USB Power Delivery 3.0 specification. usb.org/sites/default/files/2018-08/certified_usb_fast_charg…
USB-IF, USB Type-C Cable and Connector Specification, Release 2.0 (August 2019): The following order of precedence of power negotiation shall be followed: USB BC 1.2 supersedes the USB 2.0 and USB 3.2 specifications, USB Type-C Current at 1.5 A and 3.0 A supersedes USB BC 1.2, and USB Power Delivery supersedes USB Type-C Current. usb.org/sites/default/files/USB%20Type-C%20Spec%20R2.0%20-%2…