Logitech rates them at 200w rms and 400w peak power. The peak power number is totally useless and the rms rating, since it doesn't have to meet FTC power rating guidelines the way AV receiver do, is questionable but at least can be compared to other similar products.
In real life it doesn't matter. If it plays loud enough it doesn't matter how much power it has. More power doesn't make the quality of sound better it just makes it louder.