International Efficiency Marking Protocol for External Power Supplies 

This fact sheet describes the international efficiency marking protocol and its implementation 

under the ENERGY STAR Version 2.0 External Power Supply specification. Sources for additional 

information are provided on page 3. This version, updated as of October 2008, replaces an earlier 

document released in 2005. 

What is the international efficiency marking protocol? 

The international efficiency marking protocol provides a system for power supply manufacturers to 

designate the minimum efficiency performance of an external power supply, 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 external 

power supply when tested to the internationally supported test method (this test method titled “Test 

Method for Calculating the Energy Efficiency of Single-Voltage External Ac-Dc and Ac-Ac Power Supplies 

(August 11, 2004)” can be found at www.energystar.gov/powersupplies). 

What does the international efficiency mark look like? 

The international efficiency mark consists of a Roman numeral (I – VI) 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 external power supply nameplate (or an equally visible 

location).

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

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 power supply nameplate; however, exact location is at the discretion of 

the manufacturer. The text “Efficiency Level” shown below is optional. An example is 

provided below. 

How is the international efficiency marking protocol being implemented? 

The nameplate (or an equally visible location) of single voltage external ac-dc and ac-ac power supplies 

must be clearly and permanently marked with a Roman numeral from the sequence I (least efficient) to VI 

(most efficient) 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 ENERGY STAR Test Method and at each 

relevant test voltage and frequency value) 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, NoLoad, and power factor (where applicable) requirements. 

Mark Performance Requirements

Nameplate Power 

Output (Pno)

1 No- Load 

Power2

Nameplate 

Power Output 

(Pno) 

Average Active Efficiency3 Power Factor 

I Used if none of the other criteria are met. 

0 to ≤ 10 watts ≤ 0.75 0 to < 1 watt ≥ 0.39 x Pno

> 10 to 250 watts ≤ 1.0 1 to < 49 watts ≥ 0.107 x Ln(Pno) + 0.39 

II 

> 49 watts ≥ 0.82 

Not applicable 

0 to < 10 watts ≤ 0.5 0 to 1 watt ≥ 0.49 x Pno

10 to 250 watts ≤ 0.75 > 1 to 49 watts ≥ 0.09 x Ln(Pno)+0.49 

III 

> 49 to 250 watts ≥ 0.84 

Not applicable 

0 to 250 watts ≤ 0.5 0 to < 1 watt ≥ 0.5 x Pno

1 to 51 watts ≥ 0.09 x Ln(Pno)+0.5 

IV 

> 51 to 250 watts ≥ 0.85 

Not applicable 

0 to < 50 watts ≤ 0.5 for ac-ac; 

≤ 0.3 for ac-dc 

0 to ≤ 1 watt Standard: ≥ 0.480 * Pno + 0.140 

Low Voltage4

: ≥ 0.497 * Pno + 0.067

≥ 50 to ≤ 250 watts ≤ 0.5 > 1 to ≤ 49 watts Standard: ≥ [0.0626 * Ln (Pno)] + 0.622 

Low Voltage: ≥ [0.0750 * Ln (Pno)] + 0.561

V 

> 49 to 250 watts Standard: ≥ 0.870 

Low Voltage: ≥ 0.860

Power supplies 

with greater 

than or equal 

to 100 watts 

input power 

must have a 

true power 

factor of 0.9 or 

greater at 

100% of rated 

load when 

tested at 115 

volts @ 60Hz. 

VI 

and 

higher 

Reserved for future use. 

What is the relationship between the international efficiency marking protocol and ENERGY 

STAR? 

The ENERGY STAR program for External Power Supplies requires that manufacturers mark their power 

supplies using the international efficiency marking protocol. Any external power supply meeting the 

performance requirements for level V and above would qualify as ENERGY STAR (Version 2.0). Power 

supplies with performance levels of I - IV would not qualify under the Version 2.0 ENERGY STAR 

specification, which takes effect on November 1, 2008. 

The new federal US standard for external power supplies (effective July 1, 2008) is identical to level IV 

above. This standard only requires compliance at 115 V/60 Hz. 

 

1

 Pno is the Nameplate Output Power of the unit under test. 2

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

requirements. 

3

 Ln refers to the natural logarithm. 

4

 A low voltage model is an EPS with a nameplate output voltage of less than 6 volts and a nameplate output current 

greater than or equal to 550 milliamps. 
What if my power supply meets different efficiency levels when tested at different 

voltage/frequency combinations? 

To qualify as ENERGY STAR, manufacturers are required to mark the nameplate (or an equally visible 

location) with the highest Roman numeral that the external power supply meets for Active and No-Load 

requirements at both voltage/frequency combinations (115 V/60 Hz and 230 V/50 Hz). EPA also has a 

power factor requirement under its Version 2.0 specification that only applies to power supplies with 

greater than or equal to 100 watts input power and when tested at 115 V/60 Hz. 

Some organizations such as Australia’s Department of the Environment, Heritage and Arts (DEWHA), as 

well as the US Energy Independence and Security Act of 2007, have adopted a modified approach to this 

protocol, allowing manufacturers to mark an EPS capable of operating at multiple voltages/frequencies as 

meeting the requirements in only one voltage/frequency combination. This modified approach is not 

acceptable for marking a power supply for ENERGY STAR qualification, given the requirement to test and 

qualify power supplies capable of operating at multiple voltages/frequencies at both 115 V/ 60Hz and 230 

V/50 Hz. For illustrative purposes, the table below provides some sample marks and an explanation of 

each. 

Sample Marks Explanation 

Mark indicating a power supply 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 a power supply meets the level V performance 

requirements only at 115 V/60 Hz (for power supplies also able to 

operate at 230 V/50 Hz). This mark shows compliance with the US 

mandatory standard, but not with the ENERGY STAR Version 2.0 

specification. 

Mark indicating a power supply meets the level IV performance 

requirements only at 115 V/60 Hz (for power supplies also able to 

operate at 230 V/50 Hz). This mark shows compliance with the US 

mandatory standard.

Mark indicating a power supply meets the level IV requirements at only 

230 V/50 Hz (for power supplies also able to operate at 115 V/60 Hz). 

This would be relevant for the Australian and New Zealand markets as 

their MEPS and High Efficiency performance requirements and 

mandatory marking only require testing and compliance at 230 V ac. 

Dual marking for a power supply that meets different performance 

levels at different input voltages. 

For More Information 

• On ENERGY STAR: Visit the ENERGY STAR Web site at www.energystar.gov/powersupplies or 

contact Andrew Fanara, US EPA, at Fanara.andrew@epa.gov. 

• On US energy conservation standards: Visit the US Department of Energy (DOE) Web site at 

http://www.eere.energy.gov/buildings/appliance_standards/residential/battery_external.html or 

contact Victor Petrolati, US DOE, at Victor.Petrolati@ee.doe.gov.