I haven't had any experience with buying/spec-ing a 1U power supply, BUT I did stumble across JonnyGURU.com's power supply reviews....which are pretty through with tear-downs.
Here's their review of Seasonic SS-400H1U from 2009:http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=131 which seems to be really a single rail supply!
Delta DPS-500YB: http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=312
Seasonic SS-500L1U: http://www.jonnyguru.com/modules.php?name=NDReviews&op=Story&reid=276...oops, maybe a little too pricey!
It seems weird that U-NAS doesn't offer a power supply options. For the number of drives your planning on using you might want to search around for an online power supply calculator and size the PS accordingly.
Needless to say most 1U supplies are noisy. Good Luck!
Thanks I pretty sure I am going to go with the Seasonic SS-500L1U. Newegg has it for $99.99 http://www.newegg.com/Product/Product.aspx?Item=N82E16817151129
Going to need a SATA expansion card right?