Something that keeps needing to be pointed out every thread this stuff appears on: What these tools report are not functionally different from just believing "what's on the packaging", despite the misleading marketing claims.

These tools read a chip called an "eMarker". These eMarkers are programmed to say whatever the manufacturer wants them to say - there's no requirement that the information be based in reality. Plenty of cables have eMarkers that claim "40Gbps" or whatever speeds, or support 240W PD...but absolutely cannot deliver either of those. And none of these consumer level software or hardware testers can actually test either of those claims. They can only take the cable's own claims at face value.

Resistance measurements can cursorily test claims of 240W but resistance changes with temperature which changes with current...so unless your tester puts 5 amps down the wire for 5 minutes and then tests resistance it's not a very good test. AFAIK none of the testers flow 5 amps through the cable.

Actual maximum data throughput is very hard to know. The only way to really "know" how much data can flow through a cable is with an expensive oscilloscope or cable tester. Because 80Gbps cables run at ~13GHz, at minimum you need a 26GHz scope (Nyquist–Shannon sampling theorem) or more practically a 52GHz scope. And it turns out it's really expensive to measure electrical signals 52 billion times per second. The necessary devices start at $15,000 (cable signal integrity tester) [0] on the very low end and only work for max 10Gbps USB 3.2 cables, or past $270,000 for 80Gbps USB4 cables (proper 60GHz oscilloscope) [1].

On the high end, each signal integrity test device can actually cost $1-2 million [2] where the base unit starts at $670,000 plus then spending additional money for hardware-accelerated analysis, specialized active probes, and the specific PAM-3 / USB4 compliance software packages.

0: https://www.totalphase.com/products/advanced-cable-tester-v2...

1: https://www.edn.com/12-bit-oscilloscope-operates-up-to-65-gh...

2: https://www.eevblog.com/forum/testgear/uxr1104a-infiniium-ux...

WhatCable: Know what your USB-C cable can do