An electrician replaced a rotary dimmer with another one that is rated for LED GU10 bulbs. The six existing halogen bulbs connected to the dimmer weren't replaced however.
The electrician said that everything seems to work fine, and he said LED GU10 bulbs didn't work because there are currently transformers connected to each light fitting, and they need to be removed.
This is the dimmer he used: https://www.jung.de/en/online-catalogue/367389337/
I don't understand how he got the dimmer to work with halogen bulbs and I am worried that it constitutes a safety risk. The room is a bathroom, so humidity levels tend to get high during use. I am worried about fires or other problems caused by the misuse of the dimmer.
The electrician is suggesting that we remove the transformers currently connected to the halogen bulbs, and then connect LED bulbs in their place, without the need for a transformer between the dimmer and the bulbs. I agree that switching to LED lighting is the ideal course of action but I would like to verify that his understanding is correct before letting him proceed further.
The Jung brand offers a few other types of rotary dimmers: https://www.jung.de/en/online-catalogue/367389336/
Here are some photos of the spec sheet I found with the LED dimmer.