These are switch mode power supplies which mean the output is regulated to 12V(no more 14V outputs!). They take 100-240Vac 50/60Hz input and output 12V 1A. These will power most projects that don't require more than 1A of current. Center-positive 5.5x2.1mm barrel connector can be directly plugged into standard Arduino Power Jack.
They are designed to take up ONE position on your outlet strip or wall outlet. These will convert international voltage (100V-240Vac 50/60Hz) automatically; no transformer needed. Great for many electronic projects!
Wall Adapter Power Supply 12 VDC 1A(American Standard) (1 unit).