External AC adaptors plus DC-DC converters are also sold at the linitx.com store. Unfortunately, they, too, are in the UK and don't ship to the US.
The linitx.com power supply is the Lex PW002 power supply, made by the same company that makes the cool looking "bookshelf" computers for uses as routers, etc.
Anyway, to cut to the chase, the US distributor of theses supplies is
They don't show the DC-DC converter board on their website, but they do sell it.
Contact Sophia Wang, firstname.lastname@example.org
to buy. The price is $35, and they sock you with a $20 shipping fee for UPS ground, because, I suppose, they are not a retail outlet.
I bought one. I haven't assembled my computer yet, but I have plugged it in and it has powered an EPIA-M6000 board plus harddrive and CD-ROM (I don't know whether it would be suitable for heavy use of the CD-ROM; I'm just going to use mine to do a Linux install and then disconnect it.)
The power supply does seem to be silent, although I haven't taken it to a quiet room and tried to carefully assess this.
Synertrontech sent me a picture of the power supply kit before selling it to me so I could make sure that it was what I wanted. I've resized the picutre and put it up on the web:
Note that the power connectors for the drives are plugged directly into the DC converter board, rather than coming out of the main motherboard connector pin. Although this is different that what I've seen before, it worked fine for me.
Hope this helps!
P.S. A word of caution when ordering from synertrontech. First, Sophia doesn't sound like a native English speaker, so telephone communication can be a little tricky. Also,
the goofballs in their shipping department sent me my power supply and then the next day sent me another one (and billed my credit card again). Apparently someone else with the first name David ordered one the day after me, and they sent it to me. I refused the second UPS delivery, and they have promised (although I have not confirmed) that they will credit the second one back to my card.