Read the Instructions / Specifications which came with the Fixtures, as they typically will have information as to the type of Dimmers to use
(but not always...
Normally, when Dimming something with an Electronic Ballasting / Power Supply device, the basic "Simple" Incandescent type Dimmers will work.
When it comes to Dimming a Low Voltage Lamp (such as an MR-16, 12 Volt), driven by an Isolated Transformer mounted on the Fixture, then the "Electronic" type Dimmers need to be used.
Consult the Manufacturer, or check out different Dimmers' Specifications, and apply as suggested.
BTW, had to purchase a 600 Watt Dimmer, to be used with 277 VAC x 12 VAC Transformer driven MR-16 Lamps.
This one was made by Lutron, and cost around $120.00!