I use a two-color Ilford Multigrade head, which has a separate 300w halogen lamp for each color. Each lamp has its own regulated supply, to maintain the ratio of colors to the VC grade set on the head, and normalize the intensity.
All tri-color (CMY) heads that I've seen use regulated supplies. I've never used one of these.
I did use an additive tri-color head when I was printing Cibachromes ~25 years ago.
There were some early photobulb enlargers that used a Sorensen constant-voltage transformer in a box. To a casual observer it might look like a simple transformer. It did a good job of providing regulated power over a wide range of input voltages.
As with any other step in the photographic process, powering the enlarger lamp(s) is one factor that can affect final product quality.
I do have some experience with power supplies, having repaired many, and designed and currently manufacture one.