There are any number of power cords that will improve the performance of the VT100mk2. After trying a Delta Labs and a Tekline PC12, I hooked up a JPS Labs Power AC and thought: So this is the open, relaxed and extended sound I was looking for. But, as with many things in audio, you don't realize what you are missing until you try something else.
I had no idea of what the amp was capable of until I until I started to roll the tubes. Excellent detail, dynamics and imaging, and classic tube naturalness, warmth and liquidity are possible with this amp. But don't expect tube rolling to be a walk in the park.
The basic problem is that the eight Sovtek 6922s, while reliable, image poorly and are shy in in dynamics and subtle inner detail. Likewise, the Svetlana 6550 power tubes do not fully deliver a natural, warm, liquid tube sound.
The power tube problem was solved simply and inexpensively by replacing the 6550s with Svetlana KT88s (and re-biasing -- something I left to our local audio authority). For about $500 more you can buy premium tubes, but you need two matched quads and replacements may be difficult to find. Thetubestore.com will sell you the matched number-coded Svetlana KT88s, so buying replacements is not a problem.
When I tried to roll the four pairs of driver tubes, I blew up one hell of tubes and resisters. Chris at Audio Research told me I should not attempt to replace the "stand alone" pair of Sovtek 6922s located physically towards the amp's front end with any other brand, as the amp cannot be properly biased without them. But I had already found a tube that would perform in that position and not blow stuff up -- the Mullard CV5358. And I had done enough experimenting to know I didn't want the Sovteks, which from that position really limited what the amp could do. Bought the Mullards NOS from Michael Wharton at Brit Audio for about $65/pair. While the amp can be biased around the Mullards, an their huge soundstage is a big improvement over the Sovtek's rather lifeless image, they are lush to the point of sounding mushy. Matching them with three pair of relatively clincal/analytic sounding Amperex 6DJ8s (orange globe logo, Holland, steel pins) did the trick.