If it quotes it is 1000 watt with a 1100 watt max, this typically means that it will support 1100 watts all the time but it is not recommended at all and will shorten the life of the unit. It is only rated at 1000 watts and you should never go above that (as much as it supports it)... and unless you have many high end graphics cards, drives and more, you are unlikely to go above 1KW.
When you plug in a 200 watt video card, it will most likely pull about 40-50 watt idle and go up to a maximum of 200 watt if used at 100% load (if the specifications say it has a maximum of 200watt).
For the graphics card and the system in general, at 100% load (not the maximum 1100, but the supported max of 1000 watt), will most likely pull about 1,100 watts - meaning the system is using 1,000 watts along with a further 10% loss as heat.
A further example is a 1,000 watt machine with 80% efficient means it is 20% inefficient and will pull 1,200 watts.
(So to go back a bit, a 200watt card will actually pull 220 watts at 90% efficiency)
Again, remember, these are the maximums, machines fluctuate greatly whilst they are on - accessing an optical drive, being idle, moving the mouse (all be it minimal)... anything will change the wattage of the machine
2A link to the specific model of PSU would be extremely useful here. The spec sheet on the PSU would almost certainly reveal a lot more detail then just saying 1000 watts. – Zoredache – 2011-06-05T20:39:26.363
2It just means you can pull 1000 watts at all times, but if you spike to 1100 it wont blow up. – Nate – 2011-06-05T20:53:26.627
I do not have a specific model of PSU in mind - and to keep the question timeless I would rather not provide one. – darkAsPitch – 2011-06-06T03:27:26.750
2If the PSU is supplying 1000 W, and you know the efficiency at 100% load is 90%, then it is pulling ~1111 W from the wall. The extra 111 W are dissipated due to resistive component losses (i.e. heat). – Breakthrough – 2011-06-28T14:14:28.577