18,00u SLIMLINE Capacitor Discharge Unit comes with an Automatic pre-voltage power-supply module.
This means you can use ANY power supply to operate this CDU module.
Previously, the modules needed 18v to 24v to operate 100% and these voltages were difficult to obtain.
Now you can use any supply from 5v to 20v and the AUTOMATIC PRE-VOLTAGE  MODULE will deliver 26v.
One input wire of the pre-voltage module is connected to the positive of a 5v to 20v supply and the other to ground or earth or 0v  or black terminal of your supply.  
Do not connect around the wrong way or the pre-voltage module will be damaged.
The 10-turn pot has been turned fully anticlockwise to produce an output voltage of 26v, no matter what input voltage is delivered.
Fully built and ready to connect, it is the cheapest and best of all the CDU's.  You need two push switches to change the position of the point. The LED on the board shows the electrolytics are charged.

SPECIAL FEATURE
Zener diode regulation to prevent over-charging.

Contact Colin Mitchell of TALKING ELECTRONICS.com for any inquiries.
Full details on how to connect it to you layout is on the Talking Electronics website.
It is fully built with four 4,700u electrolytics and pre-voltage module for GBP6.50 ($8.50usd) and worldwide postage GBP5.60 ($7.50usd)