Both Canon 400D and Fujifilm S1500 have 10.0 MP resolution sensors but Canon 400D's sensor is APS-C (22.2 x 14.8 mm ) and Fujifilm S1500's sensor is 1/2.3-inch (6.17 x 4.55 mm ).
Since Canon 400D'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 S1500.
Below you can see the 400D and S1500 sensor size comparison.
As seen above, Canon 400D has a 11.7x Larger sensor area than Fujifilm S1500. 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.