+1 for the TDR
Sends a pulse down the cable, times how long the reflection from the other end takes to come back. IF you know the NVP (Nominal Velocity of Propagation) for the cable, then it's a simple time*speed=distance calculation. However, that's a big IF - I strongly suspect that for most power cables it's never specified. For the data cables I've installed so much of, it was part of the cable spec, around 0.7c IIRC. If you have a reasonably long piece of cable (such as a new drum) then you can test that and work out the NVP for that type of cable and it'll be near enough for similar types.
And +1 for a decent one making an NFT look cheap ? However, if you keep an eye out, you'll see used network cable testers come up on well known tat bazaars - I picked up a Fluke DSP-100 with smart remote for a good price some years ago, and whilst not doing up to date tests for network cables, it's still a really useful bit of kit for checking and fault finding.