Nordost Valhalla power cord adds jitterSince my main system isn't properly warmed up my impressions will be little flawed.
I'm using 10+ meters of stock extension strips and stock cables with my computer now. It sounds more neutral than Valhalla, it doesn't sound as bright. Stock cable sounds harsh, muddy, dark, thin and open. Valhalla sounded whiter and edgier with smooth openness, the extra whiteness made the background appear blacker and calmer, but everything was brighter and more fatiguing.
I always suspected Valhalla was colored, and I guess this confirms it. Valhalla adds some kind of jitter to the sound which makes it sound good. It also compensates for muddiness in the system. I think it removes some low-level details as well, because the background is almost too calm. It's both blacker and whiter than neutral. It gives fake dynamics. It makes everything sound more separate. It seems like Valhalla both reduces jitter and adds jitter on its own.
Valhalla must have done something to the computer which made it work badly. After my system is warmed up I will do the harddrive experiments with stock cable.