  Recent progress in observations and understanding of spectra of Seyfert
Galaxies shows that X-rays are most likely produced by magnetic flares on the
surface of the disk, similar to Solar X-ray emission. However, while the model
reproduces the shape of the spectrum well, the question of the overall
normalization of the X-ray component relative to the bolometric luminosity has
not been previously considered. Here we show that, in gas-dominated accretion
disks, the magnetic energy transport can indeed power the corona in a way
consistent with observations, {\it if} magnetic field in the disk is mostly
contained to strong magnetic flux tubes. However, in radiation dominated disks
radiation diffusion makes the field weak/diffuse, and thus the magnetic energy
transport is less efficient, i.e., in such disks the disk intrinsic emission
should be the dominant component in the overall spectrum. We compare our
findings to observations, and conclude that our theory can account for the
often observed ``steeper when brighter'' behavior in AGN and the hard-soft
spectral transitions in GBHCs.
