What is a 'Switch mode' amp

I always assumed he made them himself, although im not sure, also i think Andy has mentioned designing big (18kW) SMPS previously (in a "previous life", i think he said)

tallmike wrote:

Tony Wilkes wrote: The SM in the XP5000 is 8Kva, I would dread to think of the cost of that in the old style smiley1 .

where are these supplies made?

Sunny Gwent, why?

Tony