chematic perspective view of an example of a power supply module for mounting in the shelf of FIG. 2; [0017]FIGS. 8A, 8B and 8C are a schematic plan view and schematic perspective views, respectively, of an example of the chassis and midplane of the shelf of FIG. 2; [0018]FIG. 8D is a schematic perspective view of a part of a base member of the shelf of FIG. 2; [0019]FIGS. 9A, 9B and 9C are schema