Both Fujifilm S9400W and Fujifilm X-A10 have 16.0 MP resolution sensors but Fujifilm S9400W's sensor is 1/2.3-inch (6.17 x 4.55 mm ) and Fujifilm X-A10's sensor is APS-C (23.6 x 15.6 mm ).
Since Fujifilm X-A10's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Fujifilm S9400W.
One other difference between these two cameras that is worth mentioning is that Fujifilm X-A10's sensor doesn't have an anti-alias (Low-Pass) filter. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moiré occurring in certain scenes.
Below you can see the S9400W and X-A10 sensor size comparison.
As seen above, Fujifilm X-A10 has a 13.1x Larger sensor area than Fujifilm S9400W. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.