I bought one of the 15V Chinese Linear PSU's Stan recommended. It arrived after several weeks and works very well with my SEG and sounds as good as when using an Anker battery.
About the same time, one of the Lithium Polymer batteries I was using to power my Temple Audio monoblocks swelled and died. After some research I bought a 16AH 12V Tracer Lithium Ferrophosphate (LiFePO4) battery pack (which actually puts out 12.8V). As an experiment I connected the SEG to this as well. I have to say the combination is exceptional - more dynamic sound, much wider and deeper sound stage. At over £200 the battery is not cheap but if you need one to power other components anyway its worth a try (Tracer sell smaller batteries down to 3.5 AH for £120, this is about the same AH capacity at 12V as a 10000 mAH Li Polymer battery).
RPi3 & piCorePlayer, Ankaka Battery -> Beresford Caiman II DAC (with Venom & Gator Mod) -> Beresford Capella as Pre-Amp -> 4x Temple Audio Monoblocks ->Van Damme Black Bi-Wired to B&W 804 Nautilus and Van Damme Interconnects (everything battery powered)