Transmitting power over a distance like that would have its own problems. For instance, the most likely form the power would take is in the form of microwaves beamed down to the planet. Some of those will be absorbed by the atmosphere above the receiving station and cause problems in that way, and if the beam is not perfectly aligned you'll fry everyone who lives nearby. Plus there's the whole problem of getting all that heavy power generation stuff up into space in the first place, and also maintaining it.

The biggest issue with that whole idea, though, is why go to all that trouble to put fusion reactors in space when we have the biggest fusion reactor for light-years in any direction already pumping out power up there? Just intercept the energy coming from the Sun and beam it back to Earth in usable form and be done with it.