To sum up, by means of the adjustment plates 12 moveable in the front-rear direction (D2) on the respective panels 11 for adjustment, the mounting units 1 are compatible with different distances between the front and rear support posts 921a, 921b and different depths of the cabinet 9. Because the rails 14 can be disposed at different desirable heights, the gaps 142 between the rails 14 are adjustable. Therefore, the mounting units 1 are able to accommodate server devices designed with the specifications involving either the unit “U” or the unit “OU.” Further, by virtue of the particular arrangement of the stud-receiving holes 311 and the bridge through holes 312 in the bridge ends 31 of the bridge members 3 and the particular arrangement of the positioning studs 113a and the flange through holes 113b in the panels 11 of the mounting units 1, after the bridge members 3 assembled with the electrical busbar 41 are turned upside down, they still can be conveniently re-attached to the second panel flanges 113 of the panels 11 of the mounting units 1. Therefore, it is convenient to place the terminal member 411 of the electrical busbar 41 below or above a server device and to arrange a power supply device below or above the server device to meet different needs.