Actual Neon Transformers Came in Two Different sizes. (I have a Few of Each of these Transformers and they produce a nice Yellow Spark.)
Normally rated at Either "15Kv at 30 mA" or "15Kv at 60 mA", Both at 60 Hz Output Frequency.
They Supply these Currents, Even with a Direct Shorted Output and No Over Heating of the transformer.
These Newer Switching Supplies are at a High Frequency, They Only produce a Blue Spark.
Some only put out 10Kv and Usually at Lower Current ratings than the Original 60 Hz Transformers.
They Work Ok for running Neon Signs, But Not so good for making a Tesla Coil or for a Jacobs Ladder.