This circuit is Regulator Power Supply OUTPUT DC Adjustment 0-30V / 1A , Input is AC 9V/12V/15V/18V/24V Max.

Technical information:
   - AC input 9V ,   output DC = 1.245V to  9.62V 
   - AC input 12V , output DC = 1.27V   to  14V
   - AC input 15V , output DC = 1.29V   to  18.36V
   - AC input 18V,  output DC = 1.3V     to  22.49V
   - AC input 24V,  output DC = 1.32V   to  30V

You can also apply DC input to this circuit, in case. you already have had Fix Power Supply 12V to 33V DC. Comes with free heat sink and knob as shown in the photo  but  no AC transformer / Switch / wiring in the package

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