12V domestic halogen lamps (MR16 downlights for example, or many of the table lamps sold by Ikea) often run off 12V AC and almost exclusively now, use an electronic “transformer” (like this: https://www.bunnings.com.au/hpm-12v-downlight-transformer_p4390263). The first generation used Iron core transformers but they were prone to overheating, which combined with being chucked in a roof space sitting on paper faced gyprock under fibreglass insulation made them a significant fire hazard (at least here in Australia).
Needless to say, these electronic transformers are totally useless for monitoring voltage as required by an emonTx