2 lights 1 dimmer

Advice please..
I need to run two light fittings each with 7 x 10 watt 12 G4 bulbs on one dimmer switch? They have transformers. What type of dimmer switch do I need?
Heard lots about buzzing dimmers and overloading so want to avoid expensive mistakes.
Thanks

check the transformers can be dimmed first (it will be printed on it)

If the transformer is round and heavy, dont try dimming it, they are not normally suitable for the task. If you can, remove the transformer and fit a small electronic one, which can be dimmed.

Anyhow, if the tx's are suitable for dimming, you'll need 280 watts of dimming minimum.

Thanks for your replies.
I checked one of the transformers and it doesn’t say if it is dimmable or not, but in NEXT directory (where I purchased light fittings) it said must use NEXT halogen dimmer switch so assumed that it is. I looked at the transformer and it is electronic.
Purchased a 400W/VA Intelligent Dimmer Switch (because we didn’t want the NEXT shiny chrome one) and light fitting buzzed!
Husband is cheesed off and we are now thinking about going back to a regular switch.
What are we doing wrong? Why the buzzing?