Abstract: A stacking arrangement for at least two controllers in a powder spray system provides for the controllers to be vertically stacked one on top of the other, and an interlock mechanism between each pair of adjacently stacked controllers. In a preferred embodiment, the interlock mechanism comprises a tab and slot arrangement between each pair of adjacent top and bottom covers of stacked controllers. The tab and slot securely hold the stacked controllers together in a stable vertically aligned configuration. Locking plates are also provided to releasably secure the controllers together. The invention also provides a vertically adjustable cover mechanism for the stacked controllers. The cover mechanism encloses various lines that are connected to the controllers in the final assembly. The cover mechanism includes a vertically fixed cover part and an adjustable cover part that telescopically slides over the fixed cover part.