I'm in the U.S. and I bought a digital wall clock from the U.K. which came with an AC adapter with input 230V/50Hz/90mA and output 9V/800mA. Now I could get a transformer to convert 120V to 230V but that means connecting the already bulky adapter to another transformer and it will look hideous. Here is how far I've gotten but I'm stuck now...
The connector in the clock is a barrel type connector. First, I got a universal AC power supply for the U.S. with 120V input and an voltage output control (which includes the 9V that I need) and 1200mA output. After I received this, it looked fine and one of the barrels seemed to fit, but it required setting the correct polarity.
Next, I bought a multimeter which I got today. I set it to DC and tried both combinations of touching the black and red lines to the middle pin in the clock and to the round outer wall. When I put the black to the outside wall and the red to the inner pin, I get 0mV, but when I put black to the middle pin and red to the outer wall, I get about 1.0 mV.
Does this mean that the clock requires positive polarity or negative polarity?
Edit: Neither the power supply that shipped with the clock nor the clock instructions or case show the clock's expected polarity :( I emailed the manufacturer and they didn't answer this question.