Transformer with different kinds of loads
If you use a capacitive or inductive load, then the overall efficiency of the system will be zero, as either of those loads consume zero power, while the transformer will have losses.

The losses of a transformer are essentially core loss, which is dependent on the applied voltage, and copper loss, which is dependent on the current. At first sight it may seem therefore that for the same load current and load voltage, the transformer losses will be the same, regardless of whether the load is inductive, capacitive or resistive.

There is a subtlety that the magnetising current is in quadrature phase to the applied voltage. This means that for load currents in the order of the magnetising current Imag (that is, an order of magnitude or two less than the full power rating of the transformer), the primary current will be 2 times Imag for an inductive load, 1.4 times for a resistive load, and zero for a capacitive load, with the corresponding effect on transformer copper losses.

However, for load currents much greater than Imag, the load current will dominate the copper loss regardless of its phase with respect to Imag.