Both Canon SX270 HS and Canon G16 have 12.0 MP resolution sensors but Canon SX270 HS's sensor is 1/2.3-inch (6.17 x 4.55 mm ) and Canon G16's sensor is 1/1.7-inch (7.44 x 5.58 mm ).
Since Canon G16'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 Canon SX270 HS.
Below you can see the SX270 HS and G16 sensor size comparison.
As seen above, Canon G16 has a 1.5x Larger sensor area than Canon SX270 HS. 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.