Sort of. The RMS is the "average" voltage measured (Root Mean Squared, so not actually an average, but it gets the point across without getting in to the math.) So, taking a bunch of measurements over the duration of the sine waveform. The peak is just the highest point of that wave form. In a pure sine wave the peak is about 1.41 times higher than the RMS voltage.
The newer transformer produces what is typically referred to on the forums here as a "chopped sine wave". though pulse width modulation is the common term used elsewhere. here, rather than actually lowering the voltage the proper sine wave output is chopped off on one end for some duration. Rather than measuring RMS or peak, the amount of the wave that is cut or not cut is called the Duty Cycle. Changing the duty cycle can mean that the peak voltage is much higher while the RMS voltage is lower than compared to a pure sine wave.
The concept is a little easier to think about when used on DC power. say you have a battery that provides 12 volts of DC. if you take an RMS reading of the voltage it will be 12 volts (really 13.6 on say a car battery) which is easy to understand, as the battery constantly supplies 12 volts. If we instead apply a 50% duty cycle, the battery is on for half the readings and off for the other half so our RMS meter ends up reading only 6 volts, even though the peak voltage is still 12 volts.
How this effects the modern engines is that they all run on DC power internally, and in the electronics that convert AC from the track to DC for the electronics and can motors energy is stored at the peak voltage rather than the RMS voltage. Because of this there is more stored voltage when using a modern transformer with a higher peak voltage then when using an older one. This is also why early protosound(1) MTH engines don't work with modern transformers, they read the peak voltage from the track when determining track voltage, so only ever see full power and no power, rather than the low voltage needed to initialize the engine. Most modern engines have electronics that can recognize the desired throttle position from either power source, but there is more total power available for them to use when running on a modern transformer so the smoke will work better and the motors will run better at lower RMS voltages.