IEC 61558-2-4:2021 is available as IEC 61558-2-4:2021 RLV which contains the International Standard and its Redline version, showing all changes of the technical content compared to the previous edition.

IEC 61558-2-4:2021 deals with the safety of isolating transformers for general applications and power supply units incorporating isolating transformers for general applications. Transformers incorporating electronic circuits are also covered by this document. This third edition cancels and replaces the second edition published in 2009. This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
- adjustment of structure and references in accordance with IEC 61558-1:2017;
- description of constructions moved to IEC 61558-1:2017;
- a new symbol for power supply unit with linearly regulated output voltage.
It has the status of a group safety publication in accordance with IEC Guide 104.
This International Standard is to be used in conjunction with IEC 61558-1:2017.