They are not 1800 true Ws. The 1800 specification was what we, and other manufacturers, called "effective Watt-seconds". This was a way to equalize comparisons between more efficient mono lights to the less efficient, but familiar, pack and head systems. We no longer use the term "efective Watt-seconds", though the naming of the Alien Bees and White Lighnting systems still reflect these.

Watt seconds are an inaccurate way to measure flash output, but is the universal specification for studio flash units (though should be accurate enough for lights within the same system). Lumen-seconds would be the proper units with which to measure and compare flash output directly, though we are the only manufacturer to publish lumen second specs.

Ultra series lights predate me by at least a decade, and I do not immediately recall the actual spec, though I believe it is 640Ws. (I will update this when I can access my references).