Two ways to decouple AC from DC by using an inductor in parralel (which passed DC while leaving AC for the load with a transformer which is pretty much the same but with galvanically divided input/output and with a cap in series to restrict DC while passing AC. These topologies are often used in amps and such to decouple the DC compound and supply the load with obly AC. As you may see a cap is preferable due to the small losses that it accounts for.
