How I Test Chargers: The Watt Check Methodology

Every charger in the Watt Check series is tested the same way: same Mac, same cables, same power strip, same software readout. Here's the full rig and the reasoning behind each choice - including why the test cable is USB 2.0 and why that doesn't matter.

Every charger I test in the Watt Check series goes through an identical procedure. Same Mac, same cables, same outlet, same software readout, same order of operations. That consistency is the whole point: if the rig never changes, every difference in the numbers belongs to the charger.

This page documents that rig in full, so you can judge the results for yourself - or reproduce them. For a bare list without the reasoning, see the gear page.

Gear links below are Amazon affiliate links. As an Amazon Associate I earn from qualifying purchases. Nothing in the test rig was provided, sponsored, or discounted by any manufacturer - it’s all bought at retail. Links go to the exact products I use, except where an item has been discontinued, in which case the substitute is labelled as such.

What I’m actually measuring

Three different numbers get conflated constantly, so it’s worth separating them up front:

  • Rated wattage - what’s printed on the brick. A marketing figure, and the least interesting of the three.
  • Negotiated profile - the voltage/current contract the Mac and charger agree on out of the menu the charger advertises. This is USB-C Power Delivery doing its job, and it’s covered in depth in Monitoring USB-C Power Delivery.
  • Live draw - what’s actually flowing into the machine right now, in watts, volts, and amps.

Watt Check reports all three. The gap between the first and the last is the entire premise of the series.

The test machine

A MacBook Air M5 (16 GB RAM, 1 TB SSD), tested with the battery low. That second part matters more than it sounds: a Mac near a full charge throttles its own request and will happily sit well below what the charger can supply. A Mac with a depleted battery asks for everything it can get, which is the only condition under which you’re measuring the charger’s ceiling rather than the laptop’s disinterest.

The software readout

All numbers come from USB Connection Information reading macOS directly - no inline dongle in the path.

The app pulls live power telemetry out of the AppleSmartBattery IORegistry entry, which reports the actual measured voltage, current, and power at the USB-C port, sampled every two seconds. These are real measurements taken by the Mac’s own power management hardware, not estimates derived from the charger’s advertised rating. It also reads the charger’s full advertised profile list and the negotiated PD specification revision.

Two consequences worth knowing:

  1. Nothing is inserted into the power path. A physical USB-C multimeter is itself a component - one more set of contacts and a bit more resistance between the charger and the laptop. Reading the Mac’s own telemetry means the measurement doesn’t perturb the thing being measured. (I wrote more about why software beats a dongle in The Best USB-C Tester in 2026.)
  2. The reading is the Mac’s truth. If macOS believes it’s drawing 7.1 W at 4.9 V, that’s what the operating system is acting on, regardless of what a meter in the middle might say.

The cables

Two cables, and only two, across the entire series.

USB-C to USB-C: an Anker 240 W USB-C cable (USB 2.0, 6 ft). This is the choice that raises the most eyebrows, so here’s the reasoning.

A USB-C cable carries an e-marker chip only if it’s rated for high speed or high power. This Anker cable is rated for 240 W, which means it’s e-marked for 5 A - so it will never be the bottleneck in a charging test, no matter how large the brick. It’s also only USB 2.0 for data, which is completely irrelevant here: data speed and charging power are independent, a point that trips up a lot of people and which I’ve covered separately in USB-C Charging Speed vs. Data Speed.

Using a 240 W cable for every test removes the cable as a variable entirely. A cheaper 60 W cable would silently cap everything at 3 A and I’d be publishing the cable’s limit while claiming it was the charger’s. For more on that distinction, see USB-C 100W vs 240W Cables and E-Marker Chips Explained.

USB-A to USB-C: a Monoprice Kevlar-reinforced Type-A to Type-C cable, used for the legacy Apple bricks - either the 3-pack in black (1.5/3/6 ft) or the 3 ft AtlasFlex in white.

Unlike the USB-C side, the specific cable genuinely doesn’t matter here, and it’s worth being clear about why rather than pretending to a control I don’t need. USB-A has no e-marker and no Power Delivery. The legacy fallback these bricks use tops out at 1.5 A, which is so far below what any competent USB-A cable carries that the cable cannot become the limiting factor. On the USB-C side a cheap cable would silently cap the result; on the USB-A side there’s nothing to cap.

The power source

Every charger plugs into the same outlet: a JACKYLED detachable recessed desk power strip (6 AC outlets, 3 USB ports, surge protected). Same strip, same position, every episode - so mains conditions stay constant across the series.

That specific strip is no longer sold. If you’re assembling something similar, an Anker 8-outlet surge-protected power strip covers the same job, though it’s a flat-plug extension cord rather than a recessed desk mount. To be plain about it: this is a substitute I have not tested on, not the strip in the videos. It’s also the part of the rig that matters least - it’s mains AC feeding the charger, and every charger sees the identical source either way. The strip is held constant for tidiness, not because the brand of outlet influences a Power Delivery negotiation.

The recording rig

  • Camera: iPhone 17 Pro Max
  • Mount: an Amazon Basics 50" tripod with a quick-release phone plate
  • Fixed framing and identical shot order for every charger, so episodes are visually comparable and nothing is hidden by a convenient cut.

What I actually charge with

For transparency, since it’s a fair question - none of this is the test rig, it’s just what I use when I’m not filming:

Several of these are interesting enough to get their own episodes - the Apple 40 W adapter in particular, because a charger that advertises two different wattages has to make a decision about which one to offer, and that decision is visible in the profile list.

The procedure

Identical for every charger:

  1. Charger is placed on the desk and identified on camera.
  2. It’s plugged into the JACKYLED strip.
  3. The test cable runs from the charger to the MacBook Air, battery low.
  4. USB Connection Information is opened and the device row expanded.
  5. The rated figure, the full advertised profile list, the active profile, and the live draw are all read straight off the screen.

Nothing is re-shot to get a better number. If a charger negotiates something unflattering, that’s the episode.

Why this is reproducible

Every element above is either a consumer product you can buy or a free reading of data your own Mac already has. There’s no calibration step, no proprietary bench gear, and no measurement I can make that you can’t make yourself with the same app. If you get a different result, the rig is documented well enough that we can find out why.

Results from every charger tested with this rig are collected in Tested - one page per charger, with the full profile menu, the negotiated contract, and the live draw.