AC / DC linear unregulated adapter – the adapter consists of a mains transformer, full-wave diode rectifier (Graetz bridge) and the output filter in the form of an electrolytic capacitor. The purpose of the transformer is to provide galvanic isolation between input and output and adjustment of the voltage level. Once the voltage gets straightened you have a DC voltage with a large ripple. The filter smooths the ripple out.
AC/DC unregulated adapters are used for receivers equipped with a voltage regulator. Adapters from this group easily interact with devices for which voltage changes are not significant and are not affected by interference from the mains. These include keyboards, phones, battery chargers, illuminated advertising or drives of turntables of aerials.