Use of a digital voltmeter is the only way to confirm that your voltage is correct. Keep in mind that a transformer is reducing your primary voltage (house current) as a percentage. The transformer is not a regulator … a regulator would supply a constant 12 volts, no matter the primary voltage. Every installation is unique due to the variations of our power grid.
For LED installations, consider utilizing our IL200.515 electronic LED transformer. It automatically adjusts for the load and increases the product and system reliability. Visit Electronic LED Transformer for more information.