I was researching this and thought it could use its own thread. I'll fill in the gaps later as best I can. Feel free to contribute info if you've got it!
White PC Engine, Core Grafx I & II, Shuttle
MODEL: PAD-105/PAD-106
Output voltage: 9V
Rated current:650mA
Polatrity: Center negative
Plug size:Outer radius 5.5mm, Inner radius 2.1mm
Smoothing capacitor: ??
Supergrafx
MODEL: PAD-113
Output voltage: 9V
Rated current:800mA
Polatrity: Center negative
Plug size:Outer radius 6.3mm, Inner radius 3.1mm
Smoothing capacitor: ?? (package is sealed; maybe a clamp can open it?)
Super CD-ROM2
MODEL: PAD-125
Output voltage: 12V
Rated current:1000mA
Polatrity: Center positive
Plug size:Outer radius 6.3mm, Inner radius 3.1mm
Smoothing capacitor: 16V 10000uf, 2cm diameter, 3.5cm height
Duo-R/RX
MODEL: PAD-129\PAD-130
Output voltage: 9V
Rated current:1000mA
Polatrity: Center positive
Plug size:Outer radius 5.5mm, Inner radius 2.1mm
Smoothing capacitor: 16V 4700uf, 1.5cm diameter, 3cm height