The "minus sign above 3 dots" is a graphical symbol to indicate DC
output. The corresponding symbol for AC would be one cycle of a sine wave.

Since the output is DC, there will be one (or two) rectifier diodes
inside. There MAY also be an electrolytic filter capacitor, and beyond
that, there MAY be a regulator (zener) diode or a regulator IC. Or, the
filter cap and regulator might be inside the disc unit.

Since you say you can open the case, tell us what is in there.

Bill
=======================

Vic wrote:

Would appreciate some advice on the above. The adapter was part of a "Dual
record deck" (CS455). Unfortunately the adapter cable was damaged and it
no
longer works. Does anyone know what one I could use as a replacement for
the
"Dual deck"?

The information on the AC Adapter is:
Input: 230V~ +-10%/50Hz/1VA
Output: 12V-/20mA
Type: FW3099

Output: 12V-/20mA

(The Minus- sign after the 12V is placed above 3 dots...)

It can be taken apart as it is fixed together by two screws. There is
no other information on the inside.