First of all thanks for your extensive contributions to this subreddit. New Valve Index user here, and I purchased both of your linked cables for my extension purposes. Unfortunately the one you linked for power here does not fit the Index's wall adapter, its female end internal needle is too large for the hole inside the Index's wall adapter's male needle.

From the valve developer community: "The dimensions for the female plug (PSU side) are 3.5mm Outer Diameter (OD) and approx. 1.1mm Inner Diameter (ID) and for the male socket (HMD side) are 3.6mm OD and 0.9mm ID. A most common 3.5mm/1.35mm plug/socket DOES NOT FIT! Thank you Valve for using such a rare and uncommon size!"

On the hunt for a 3.5mm/1.1mm extension cable. Amazon seems to only have one here and it's OOS, and of the two reviews one said it worked for their index cable, one said it damaged their index cable. Only other option I've found was Walmart Canada...

Edited for clarity.