As Elberoth2 said the power transformers are hidden in the amplifier bottom behind a cover. They use large but slim toroidal power transformers. I hosted the AW180s (the little brothers of the AW400) for some time and they are wonderful amplifiers. Choice will depend mainly on system and taste.
Electrocompaniet class D ?
The Electrocompaniet AW400 power amp , there is nothing in the specs or reveiwes about class D or digital output , the amp discription calls it push pull solid state , when I saw pictures of its internals there was no visable transformer just a whole lot of caps . A 400w class AB amps power supply should be clearly visible . If anyone can shine some light on this it would be much appreciated .