unknown rack PSU ("PPI 1247-000-91 ADDS")

[Jules Richardson]

I found a vintage rackable linear PSU at a sale over the weekend, appears 
to be late '70s vintage going by date codes on some of the high-power 
components inside.

Front panel is plain black with just a power switch and telltale lamp.

Back has a ratings sticker which says "PPI 1247-000-91 ADDS".

Outputs are +24V at 3A, +12V at 2A, +5V at 30A, -12V at 4A.

Ring a bell with anyone? I'm familiar with ADDS in a terminal context, of 
course, but this lump is obviously for something larger - perhaps a 
"washing machine size" fixed/removable drive unit or similar, but I'm 
surprised there's not obvious branding on it if so.

cheers

Jules