12v linear power supply

Automotive battery should be pretty good for that. Some of them can last before recharging driving your preamp for months.

Get simple low-current charger for it and you're all set 

Little more but Teddy Pardo is an excellent LPS. I have one with my RME-ADIFS and there is a noticeable difference.

PLEASE insist upon a power supply with a fuse on the output. That especially includes a power supply based on a battery.

Otherwise you may find that power supply to be very expensive indeed.

Swagman makes excellent linear PSU’s. I bought an 18VAC one, and it’s built well and works well. Hope that’s of help. Good luck! 

i do like the auto battery idea. likely superior to almost any LPS. But big, ugly, and requires a charger.

as to LPSs - DACs are relatively low powered in general; but if you are powering a USB bridge or Raspberry pi or similar, those require much higher current, and a surprisingly large amount during boot up.

You might share more about the device, what you have now, and what issues you are trying to resolve (or improve).

I do think an LPS makes a difference. I designed and built one for pretty much every digital device i have-- and an upgrade for the one DAC that kinda needed such.

G