The ZS’s voltage input range is from 9V to 15V which means it will re-regulate it internally. The result could be better, or worse (if you spend $$$$ on a power supply by cost-vs-effectiveness perspective). So I personally think just go with the power supply unit shipped with original package, or no more than iPower 2.
This has made my system sound significantly better - cleaner, more open and dynamic, and video is better to. Mine powers the Zen, a TiVo, my router and a Fire stick. I tried the Zen on the 12v tap but prefer the sound at 15v
If you have multiple DC powered devices, the HD Plex is worth a close look. Note that the fixed outputs can be customized for your needs. Mine has two 12v taps
Wow that power supply is about 3x the price of the stream . But it does run 2 devices at least. It seems to be a wonderful LPS
I put a new iFi ipower X 15v on my Stream last week, but I already had the launch version of the Stream with the good power supply, so I do not hear any real difference, but I know it’s there which is the important thing
Not sure if it is a little bit late, but you could try the Silent Angel Forester F1 or the clone from nuPrime LPS 205. They are both between 450-500 Euro for a new one, but you can get them cheaper used, and sometimes they are somewhere on offer.
Edit: I saw that they both only provide 5V, so forget about it. You’d need something from Keces instead (like a Keces P3).
Actually, I got a iFi Zen Stream now and attached it to my Keces P8 Dual 12/19V via the 12 volt output (I have a PrimeMini4 on the 19 volt output and a Silent Angel N8 on the 5 volt USB output). Sounds nice, and audibly better than the supplied cheap power supply.