computer enclosure 30 the second switching power supply 52 has a smaller mating face 54 than the first switching power supply 40 has and therefore the mating face 54 does not block the entire opening 46 like the mating face 48 of the first switching power supply 40 does a cover 56 is secured to the rear panel by a screw 58 which covers the portion of the opening 46 not covered by the power supply 52 the switching power supply 52 is fixed to the cover 56 and the rear panel 36 by screws 60 as shown in fig4 and 5 the cover 56 includes a vertical portion 62 and a horizontal portion 64 a step portion 66 is defined along an upper side of the vertical portion 62 the step portion 66 extending downward to define a bay zone 68 for accommodating a tab 72 extending from an upper edge of the opening 46 the bay zone 68 and the tab 72 respectively define a hole 70 and a second hole 74 which align with one another the cover 56 further forms a pair of stoppers 76 projecting forwardly and extending outwardly from opposite sides of the vertical portion 62 for abutting an exterior surface 78 of the rear panel 36 around the opening 46 in the lower portion of the vertical portion 62 the cover 56 forms.