Yes, pulse shape can suffer degradation in passage through a cable, but a pulse constitutes a single bit and DACs do not operate on individual bits (not even DSD).
They operate on groups of 16-32 bits (PCM mode). The timing structure is based on the boundaries of those bit-groups (bytes).
Plus, the bits do not go directly from cable to DAC - there is always a USB interface circuit (XMOS or similar) in between that also serves as buffer
This decouples the timing jitter of source (PC) from that of sink (DAC).
Yes, dirty power is very real thing and can manifest in raising the noise floor of DACs.
Implementers have to make some seriously rookie mistakes or neglectful practices to miss cleaning that up before the DAC sees it.
Also, note that is quite a different effect from
signal errors.
You are right in that a quality cable is important to maintain fidelity.
But if you have a system where source noise is coupled and audibly influential to the audio signal, cable/wire quality will have little to no effect on mitigating that.
Unless it's a ground loop somewhere, but that can be trivial to fix.
I have to hope you are just butchering that sentiment
How does a cable have any sound at all? It's a passive element.
