It should work i think when i did the math it was 0.6a but you would be better with 12v 5a power supply. If you over volt you destroy the gridseed example anything above 12v. If you under amp you destroy the power supply and that in turn may cause a problem with the gridseed. You need to make sure it is center positive and gridseed can use either 2.1mmx5.5 or 2.5x5.5 end.
See this item
http://www.ebay.com/itm/180747689119?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649