I’ve just discovered this incredibly useful app – WhatCable.
What this app does is interrogate your Mac’s USB ports via IOKit to show their properties. The port can report whether or not anything is plugged in, and if something is plugged in, it will tell you the capabilities that the cable or device has requested.
WhatCable can show you all of this information including the headline specs for the cable (e.g. Thunderbolt / USB4, USB device, Charging only, Slow USB / charge-only cable), if the Mac is charging through that port, how much power is being drawn and what the limiting factor is (e.g. does the cable only support slow charging, or is it a high-power cable but the Mac is requesting less power as the battery is nearly full), and any information reported by the E-Marker chip in the cable.
Not all cables have E-Marker chips, generally cables that are capable of carrying 60W or more for Power Delivery will have one, as will cables that can do higher data rates, e.g. Thunderbolt and USB 4 cables.
Some cables have E-Marker chips that lie, be aware that this app will only report what the chip says, it won’t actually test the cable to see if it’s capable of doing what it reports it can.
WhatCable uses USB-IF’s published list of Vendor IDs (VIDs) which is, annoyingly, published as a PDF with a link that changes every time they release a new update. You can find the latest version on the USB-IF Developers page if you care to seek it out.
If a connected cable has a VID that doesn’t appear in the list, it’ll be flagged. Just like the E-Marker chip however, there’s nothing to stop an unscrupulous vendor from using a someone else’s VID, take this with a grain of salt too.