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People are going for GU10 LED's now. If you need to change from 12v Halogen to LED and want a relatively cheap and simple pathway then the Integral Evofire frame is great, there's a version which works with insulation or one without.
They are IP65 and fire rated and also fit any hole from 70mm and have a 100mm bezel to cover the issues you get when pulling the old downlight frames out of a ceiling. Just add a GU10 led dimmable lamp in warm or cold white.
So a bit of reading tells me that 12v ac was the old halogen standard, some leds will work with old ax halogen drivers, but dc is the newer standard and most led bulbs will be dc.
This is why I hate domestic.