Note on testing:

If you want to check the transformer when you receive it, we recommend to connect LED light directly to output to confirm it works.
Testing with a voltmeter: To test the transformer, you must apply a minimum watt/12v load before measuring
AND you must use a special "true RMS" voltmeter.

A standard AC voltmeter cannot measure the output of a high frequency electronic transformer.
If you test without loading the transformer or without using a "true RMS" voltmeter, you may get no voltage or an incorrect low voltage (i.e. 2.3 VAC or 2.92 VAC).
Only when you connect load to output the check by tester will display 12v output.