mA is the abbreviation for milliamps.
It relates to the minimum current and power capacity required of the transformer. (.45 Amps and just under 11 watts).
You might want to Google the manufacturer of the carousel to see if you can get an original part.

Without getting into all the technical details of power supplies and transformers at the moment, and agreeing with randy427's reply, I'd suggest one other source. Home sprinkler and timers use 24 VAC, usually under 1000 mA, and replacement plug-in wall transformers (smaller ones) can usually be found at Lowes/Home Depot. The interconnect may be an issue if there is a plug-in connector but if you can access the internal wires, it's just wire-to-wire (polarity doesn't matter) - and can be done with some small wire nuts.

Any power suppply that is 24 volts AC and 450ma or greater will be fine to use for this. Finding a plug to match the unit could be a problem.

If the marking is as described, the supply (actually just a transformer) will need to be significantly larger than the devices current (often at least 2x).

A thermostat transformer should be just fine for this low power (many are around 2 amps, but your device will only pull as much current as it requires to operate).

My spouse bought a whole basketful of transformers. Dozens of them, literally a basket full, from a thrift store for four bucks. We found what we needed and saved $19.97 plus S&H and still have about two dozen transformers and a basket.

I was at Lowes this morning picking up some outdoor pipe insulation and was in the same aisle as irrigation timers. They had the Orbit brand 24VAC/750mA replacement transformers I was referring to earlier - they were $14.97 - I wrote down the Lowes SKU number but their website doesn't show it for some reason. Here is a link to Orbit's website which shows the product, it or a similar product should work just fine. You should be able to find a plug-in transformer (often called a wall-wort) like this at most hardware stores. It has two bare wires on the end of the output which will need to be wired directly to the carousel.

Here is a link that might be useful: Orbit replacement xfmr

Wanted to let everyone know how much I appreciate their help on this.
It Really pays to comparison shop.
I found what I needed and after looking at dozens of sites and going to a lot of stores .. Here (link) is the adapter/transformer I chose.

Boy .. The prices varied from $30.00 to $5.00!

Thanks Again Everyone!

Here is a link that might be useful: BPH