An exemplary fuel cell device assembly is a fuel cell stack assembly comprising: (i) a plurality of fuel cell packets, each of the packets comprising (a) a frame and (b) two planar electrolyte-supported fuel cell arrays, the fuel cell arrays arranged such that anode side of one fuel cell array faces the anode side of another fuel cell array, and the frame in combination with the fuel cell arrays defines a fuel chamber; (ii) a main enclosure enclosing the plurality of fuel cell packets, such that the plurality of packets form a plurality of oxidant channels; (iii) a restrictor plate forming, in conjunction with the fuel cell pockets, a plurality of oxidant channels; (iv) an inlet oxidant plenum manifold connected to one side of the oxidant channels; (v) an outlet oxidant plenum manifold connected to the other side of the oxidant channels; (vi) an inlet fuel manifold connected to one side of each of the fuel chambers; and (vii) an outlet fuel manifold connected to the other side of each of the fuel chambers.