What does the Roman numeral on a charger label, such as VI, mean for US energy rules?

Main answer · Wecent Editorial Team

Short answer: The numeral shows which efficiency level the external power supply is declared to meet. Level VI is the current US Department of Energy level for most external power supplies, and Canada has aligned rules. If your charger is in scope, the marking and the test data should be there. Ask suppliers for the test report and check the official pages for the scope.

What it is

Efficiency rules for external power supplies, such as plug-in chargers, set minimum efficiency and maximum no-load power. The efficiency levels are numbered, and the numeral on the label shows the level the supplier declares the product meets.

The US and Canada

In the United States, the Department of Energy sets the standards for external power supplies under 10 CFR 430.32(w), and the current level for most covered products is Level VI. Natural Resources Canada has its own regulations for external power supplies, with a similar approach. Check the official pages for the product types in scope and for any exclusions, because not every charger is covered in the same way.

What a buyer should check

• The marking. It should be on the product, where required, and should match the report.
• The test data. Ask for the measured efficiency and no-load power.
• The report. It should come from a competent lab, using the required test procedure.
• The scope. Confirm whether the product is covered, for example by output type and power.
• The model. The report should match the exact model, not a similar one.

A common mistake

A numeral on the label is a claim, not proof. Some products carry a mark without a proper report behind it. Ask for the evidence before ordering.

For importers

Importers have their own responsibilities for compliance. Keep the reports on file and read the Department of Energy’s importer information.

Quick summary

The numeral shows the declared efficiency level. Check the scope, the marking and the test report for each model.

Questions to ask suppliers

Which efficiency level does this model declare? Which test procedure and lab produced the data? What are the measured values at each loading point and at no load? Does the report match the exact model and output? Written answers to these questions help you avoid surprises at import or in an audit.

Sources checked on 24 Oct 2026: U.S. Department of Energy: External power supplies; eCFR: 10 CFR 430.32 Energy conservation standards; Natural Resources Canada: External power supplies.

Where this answer says to confirm with Wecent, the detail is not published on the product page and has to come from the datasheet or the factory. General facts come from the regulators, standards bodies or device makers named in the text.