International Efficiency Marking Protocol for External Power Supplies 

Version 3.0, September 2013 

This fact sheet describes the international efficiency marking protocol for external power supplies (EPSs) 

developed by the U.S. Environmental Protection Agency and now maintained by the U.S. Department of Energy 

(DOE). Sources for additional information are listed at the end of this document. This version, updated as of September 

2013, replaces an earlier document released in October 2008. 

What is the international efficiency marking protocol? 

The international efficiency marking protocol provides a system for EPS manufacturers to designate the minimum 

efficiency performance of an EPS, so that finished product manufacturers and government representatives can easily 

determine a unit’s efficiency. This mark does not serve as a consumer information label, but rather demonstrates the 

performance of the EPS when tested to the internationally supported test methods. (See For More Information on 

page 3 for references to these test procedures.) 

What does the international efficiency mark look like? 

The international efficiency mark consists of a Roman numeral that corresponds to specific minimum Active and No-Load 

efficiency levels (as well as a power factor requirement for level V) and is printed/applied by the manufacturer on the EPS 

nameplate, product packaging, or accompanying documentation.

Format: Roman numeral: I, II, III, IV, V, VI, etc. 

Font: Times Roman preferred (or other plain serif fonts). 

Size: Legible and indelible. 

Color: Text to contrast with the nameplate background, unless incorporated in the case molding. 

Placement: Preferably on the EPS nameplate; however, placement on the product packaging or accompanying 

documentation is also acceptable. The exact location is at the discretion of the manufacturer. The text 

“Efficiency Level” shown in the example below is optional. 

How is the international efficiency marking protocol being implemented? 

The nameplate, product packaging, or accompanying documentation of ac-dc and ac-ac EPSs must marked with a 

Roman numeral that corresponds to specific minimum Active and No-Load efficiency levels (as well as a power factor 

requirement for level V). The performance requirements for each Roman numeral are shown in the table below. 

To determine the appropriate Roman numeral, manufacturers: 1) compare the unit’s Active, No-Load, and power factor 

test data (when tested in accordance with the appropriate single-voltage or multiple-voltage test method1) with the 

performance requirements at each level of the Roman numeral scale; and 2) choose the highest Roman numeral where 

the power supply meets the Active, No-Load, and power factor (where applicable) requirements. 

 

1

 Note that some jurisdictions have additional sampling requirements that must be met when testing products. 
2

Mark

Performance Requirements

Nameplate 

Output Power 

(Pno)

2

No-Load Mode 

Power3

Nameplate 

Output Power 

(Pno)

Average Efficiency in Active Mode4Power Factor

I Used if none of the other criteria are met.

II

0 to ≤ 10 W ≤ 0.75 0 to < 1 W ≥ 0.39  Pno

Not Applicable

 10 to 250 W ≤ 1.0

1 to < 49 W ≥ 0.107  ln(Pno) + 0.39

 49 W ≥ 0.82

III

0 to < 10 W ≤ 0.5 0 to 1 W ≥ 0.49  Pno

Not Applicable

10 to 250 W ≤ 0.75

 1 to 49 W ≥ 0.09  ln(Pno) + 0.49

 49 to 250 W ≥ 0.84

IV 0 to 250 W ≤ 0.5

0 to < 1 W ≥ 0.5  Pno

1 to 51 W ≥ 0.09  ln(Pno) + 0.5 Not Applicable

 51 to 250 W ≥ 0.85

V

0 to < 50 W AC-DC: ≤ 0.3

AC-AC: ≤ 0.5

0 to ≤ 1 W Basic Voltage: ≥ 0.480  Pno + 0.140

Low Voltage5: ≥ 0.497  Pno + 0.067

EPSs with ≥ 100 

watts input power 

must have a true 

power factor ≥ 0.9 

at 100% of rated 

load when tested 

at 115 volts/60Hz.

> 1 to ≤ 49 W Basic Voltage: ≥ 0.0626  ln(Pno) + 0.622

Low Voltage: ≥ 0.0750  ln(Pno) + 0.561

≥ 50 to ≤ 250 W ≤ 0.5 > 49 to 250 W Basic Voltage: ≥ 0.870

Low Voltage: ≥ 0.860

VI

Single-Voltage

Not Applicable

0 to ≤ 49 W AC-DC: ≤ 0.100

AC-AC: ≤ 0.210

0 to ≤ 1 W Basic Voltage: ≥ 0.5  Pno + 0.16

Low Voltage: ≥ 0.517  Pno + 0.087

 1 to ≤ 49 W

Basic Voltage: ≥ 0.071  ln(Pno) − 0.0014  Pno

+ 0.67

Low Voltage: ≥ 0.0834  ln(Pno) − 0.0014  Pno

+ 0.609

 49 to ≤ 250 W ≤ 0.210  49 to ≤ 250 

W

Basic Voltage: ≥ 0.880

Low Voltage: ≥ 0.870

 250 W ≤ 0.500  250 W ≥ 0.875

Multiple-Voltage

Any ≤ 0.300

0 to ≤ 1 W ≥ 0.497  Pno + 0.067

 1 to ≤ 49 W ≥ 0.075  ln(Pno) + 0.561

 49 W ≥ 0.860

VII Reserved for future use.

 

2

 Pno is the Nameplate Output Power of the unit under test.

3

 In Australia and New Zealand, AC-AC external power supplies are not required to meet the no-load mode power requirements.

4

“ln” refers to the natural logarithm.

5

 A low-voltage model is an EPS with nameplate output voltage of less than 6 volts and nameplate output current greater than or equal 

to 550 milliamperes. A basic-voltage model is an EPS that is not a low-voltage model.
3

What if my EPS meets different efficiency levels when tested at different voltage/frequency combinations? 

Some organizations allow manufacturers to mark an EPS capable of operating at multiple voltages/frequencies as 

meeting the performance requirements in only one voltage/frequency combination. For illustrative purposes, the table 

below provides some sample marks and an explanation of each. 

Sample Mark Explanation

Mark indicating EPS meets the level V requirements at both 115 V/60 Hz and 230 V/50 Hz, if 

designed to operate at multiple input voltages. Products with a nameplate marked for only one 

voltage and frequency should also use this mark, assuming the product meets the performance 

requirements; in other words, manufacturers do not have to indicate the voltage with the mark.

Mark indicating EPS meets the level IV performance requirements only at 115 V/60 Hz (for 

EPSs also able to operate at 230 V/50 Hz).

Mark indicating EPS meets the level IV requirements at only 230 V/50 Hz (for EPSs also able 

to operate at 115 V/60 Hz). 

Dual marking for EPS that meets different performance levels at different input voltages.

For More Information 

 Test methods for single-voltage and multiple-voltage EPSs: Title 10 of the U.S. Code of Federal Regulations, 

Appendix Z to Subpart B of Part 430. Available from the U.S. Government Printing Office at www.ecfr.gov.

 U.S. energy conservation standards for External Power Supplies: Visit the DOE website at 

http://www1.eere.energy.gov/buildings/appliance_standards/index.html or e-mail the U.S. DOE at 

battery_chargers_and_external_power_supplies@ee.doe.gov.

 ENERGY STAR: Visit the ENERGY STAR website at www.energystar.gov/powersupplies