No Alan, let's not mislead anyone. The KW doesn't put out 25 volts, and it's not more powerful than a ZW. At ~20V open circuit, 18 volts full rated load, and 10 amps continuous (across all channels), the ZW was the most powerful postwar transformer. The prewar Type Z (with four dials on its face) was rated at 250 watts, and COULD output 24 volts. The only postwar loco that was specifically rated for 20 volts is the 773 Hudson (although a dual-motored diesel pulling 5 lighted aluminum cars could draw several amps.)
None of these vintage transformers can match the Z4000 for power, or for its quick-acting circuit breaker and reliable whistle activation. But... Lionel command circuitry is rated for 19V absolute max. So turning any transformer up beyond that is asking for trouble. And the feel of the handles on the Z4000 is like sliding plastic, yuck! It just doesn't compare to the positive tactile sensation of the roller moving across the windings on an original ZW.
Another good choice in a modern transformer is the ZW-L. It's output depends upon the connected bricks, up to a total of 620 watts!