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Linux has a very nice and super informative way to do this too: https://github.com/Rajaram-Regupathy/libtypec/wiki/lstypec-:...

It relies /sys/class/typec: https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-c... which does not always exist https://bbs.archlinux.org/viewtopic.php?id=274618 https://community.frame.work/t/tracking-controlling-power-di... https://www.reddit.com/r/UsbCHardware/comments/z92jgf/when_d... etc.

> Linux has a very nice way to do this [...] which does not always exist

Some things never change haha

You can get this information from the "System Information" app in macOS as well. (At least, that's what it's called in Ventura...)

It should be under Hardware -> Power, in the section titled "AC Charger Information".

You should also be able to see connected USB-C cable capacity under Hardware -> USB. For example, mine says the following:

  USB 3.1 Bus:

    Host Controller Driver: AppleT8112USBXHCI

  USB3.0 Hub:

    Product ID: 0x0813
    Vendor ID: 0x2109  (VIA Labs, Inc.)
    Version: 90.11
    Speed: Up to 5 Gb/s
    Manufacturer: VIA Labs, Inc.
    Location ID: 0x01200000 / 2
    Current Available (mA): 900
    Current Required (mA): 0
    Extra Operating Current (mA): 0

  USB2.0 Hub:

    Product ID: 0x2813
    Vendor ID: 0x2109  (VIA Labs, Inc.)
    Version: 90.11
    Speed: Up to 480 Mb/s
    Manufacturer: VIA Labs, Inc.
    Location ID: 0x01100000 / 1
    Current Available (mA): 500
    Current Required (mA): 0
    Extra Operating Current (mA): 0

Any way to do similar for DP/HDMI? I've thrown away multiple cables cause I couldn't tell if the cable was just old and didn't support what I needed vs somehow broken. Looking at system report I only see `Graphics/Displays` which show's monitor capabilities but not cable. (I'm not actually sure if DP/HDMI advertise their capabilities in the same manner as USB 3).

Much like GP I've taken to labeling newly bought cables with a label maker to avoid wasting them in the future due to being unknown.

There’s an okay video from LTT where they hire or buy an expensive tester for HDMI cables. Seemed to be a a bit of a dark art.

yeah I've seen that, would be awesome to have access to it but not worth the cost to me, was less interested in stress testing does this 100% meet spec and more interested in "this labels itself as HDMI v{X} with optional features {y}, {z}".

I mostly care as my current monitor requires HDMI 2.1/Display Port 1.4 and going through my random cables drawer was extremely tedious. As I had way to many cables.

DP and HDMI cables are mostly passive with no identifying chip, so the only way to determine their bandwidth electronically is to try to bring up the link at that speed.

There should be no such thing as a 15 watt cable, by the way.

Every cable is a 60 watt cable by default. 20 volts, 3 amps.

Cables designed for 5 amps have a marker chip in them. If they follow the old spec they support 20 volts, and if they follow the new spec they support 48 volts. There's not much incentive to fake these because you still have to put a chip into it and 60 watts is fine most of the time.

Anecdotally I was able to get this command to return 8 watts by using a usb-A -> usb-C cable meant for charging a mouse.

That sounds like you're hitting the limit from non-charging ports. Normal A to C should allow much more. But either way that's a special case here, because the limits are entirely on the USB A end. That's not a proper C cable.

An A-to-C cable is limited by what an USB-A host can supply, since that's the limit which a compliant C-device sensing an A-to-C cable or adapter would observe.

Depending on the combination of host and device, that would be 4.5W for standard USB 3, 2.5W for USB 2, up to 7.5W for USB Battery Charging (BC), or possibly more for non-USB-C PD (highly unlikely, since it would require legacy PD signalling on the voltage pins, which almost no USB-C devices support as far as I know).

I strongly suspect it's USB BC, rounded up to 8W by Apple.

As an aside: Apple's USB power controllers used in their laptops are surprisingly flexible based on my observations: In addition to the obvious USB-PD, they support at least USB BC and Apple's proprietary USB-A resistor-based protocol. I was able to successfully charge a MacBook Pro at 12W and even 5W supplied by an old iPad/iPhone charger and the appropriate combination of adapters once.

Great post thanks for the information. Seems to verify my experiences.

I’m actually able to run my m2 MBA from a 5w usb a iPhone charger. I thought that was cute.

Apparently, USB-C cables are supposed to contain an “e-marker” chip that can tell you its bandwidth, wattage, and other specs. It would be nice if this information showed up somewhere when you plugged in an empty cable into your Mac.

But that only helps if you plug it into something. Better would be a visual indicator that can be used when the cable is just lying around unplugged.

I’ve also tried to get that information on macOS before, but annoyingly all promising (i.e. related to the SOP protocol which is how the computer talks to the chip in the cable) log lines seem to be redacted.

This is doubly frustrating in that it shows that it’s clearly available to the OS (and not handled by a lower layer controller), but also leaves the faint hope that Apple might implement just such a feature in the future.

My suspicion is that this is security related. I'm on the lookout for a brand-name quality Thunderbolt-capable cable with an LCD showing current power.

Who's security? Is Apple trying to protect me from the information that my $20 USB 4 cable is just as good as their own $69 version?

The system logs are redacted by default as they were a common source of information leakage. You can enable unredacted logs with a configuration profile: https://superuser.com/questions/1532031/how-to-show-private-...

> So, you kinda need a charger that meets or exceeds the power delivery of the cable you're testing. And I believe this relies on the cable's self-identified capacity via the e-chip or whatever, so it could be fraudulent? But it's better than nothing.

Get a cable with a watt meter display included. I use that on my Fold: https://csdvrx.github.io/ section 0.4 : https://csdvrx.github.io/X1_Fold_(20RL_20RK)_Optimization/pa...

Such cables cost about $10 on amazon, or $2 on aliexpress. Amazon link for the reference: https://www.amazon.com/Charging-Display-Braided-Compatible-G...

These can be useful, but ultimately a watt meter tells you what the device is actually using at the moment, which is not only limited by the cable and source capabilities, but also by the power sink device's current needs.

Mcdodo isn’t a member of the USB IF group and their products aren’t certified. I wouldn’t have much faith that the number in the display is correct.

Thanks. Now I'm a bit freaked out to realize that tiny CalDigit PD cable is rated to 100W. Yikes. The future is wild.

For a cable 1-2 meters long, a conductor 1mm across is more than enough to carry 5 amps.

The whole cable is smaller than 5mm diameter. Less rubber jacket, and shield, it might just be 3mm inside. And there are ~18 lines in there? I expect the power lines are larger than the differential signalling lines, but I'm just realizing how much I'm trusting this vendor.

That's much more than big enough. 1mm diameter was the overkill number, and 3mm diameter is nine times as big while you only need two of them. Even accounting for insulation and the smaller data wires, that's plenty.

I compare my solid core romex 11-2 rated for 15A to my sexy T3 cable rated to 5A, and my instincts are not reassured.

The romex has to go a lot further than 1-2 meters. Also it has pretty thick insulation.

The difference in distance combined with USB having a 5 amp limit gives you at least a 10x difference in necessary conductor cross section.

11 gauge wire is 2.3mm across. Divide the cross section by ten and you have 21 gauge wire, which is .7mm across.

Looks like PD spec varies voltage all the way up to +48V which supports 240W of power, so 5A@48V.

Using a calculator like at https://www.omnicalculator.com/physics/wire-size a 1m cable with a relatively user friendly max wire temp of 40c asks for a diameter of 0.6mm. Looks like there is 4 VBUS pins and even tho it's reversible I imagine for full power it requires all 4 (or all 4 must be connected to "support" the spec).

In theory you could have reduced wire diameter and spread current across the 4 VBUS wires, or have a single wire of the correct diameter and then connect to all 4 VBUS at the connector but everything is stranded wire in those cables anyway and I assume there's some complex maths to do to figure out the best for it.

It is super freaking cool, though. It makes me wonder if many household appliances can't just use usb c. I don't know how much further they can raise the voltage beyond that though seeing as there's all the electrical safety rules on conductor spacing etc to avoid arcing/flash over.

I've been using a nice Brother labeler for years to label all my power plugs. eg this power plug goes to this router etc. since a lot of them are subtly different.

I once mixed up two different netgear router power plugs - a new version and an older version. I had the newer netgear router hooked up to the old plug - which gave slightly less amperage - and everything worked fine until it would randomly die. It took me a long time to figure out that it was dying when it was under load and trying to pull more power than was available.

I've also started doing this, with USB-C to C cables you might want to get something like the C2C caberQU cable tester as a lot of cheap type c cables don't actually wire all the conductors.

Also I like to note the cable length on the label, measured by myself since manufacturers always count the connectors on the total cable length and on some of them that can add up to almost 10cm

C2C caberQU is very useful

That tells you wattage but not transfer speed - e.g. most 100W power USB-C cables are USB2.0 (yes, Apple ones too).

To you have a matrix - charging speed and capability.

This is incredibly helpful, thank you