AL electric field strength

Be aware that electric field intensity E equals to the negative of the potential gradient, i.e. E = -dV/dx

This relation applies to all situations, whether the electric field is uniform or not.

It is only that in the case of a uniform electric field, the value of dV/dx is constant with respect to space. In the case of non-uniform field (e.g. that given by point charges), the value of dV/dx varies with space.