Comparing Power Supply Reliability: Ask Beyond the MTBF Number

Keep three purchasing questions separate

A large MTBF figure can look persuasive in a quotation, but it does not answer how long a particular adapter will last in your equipment. Bel explains that MTBF is a statistical reliability measure rather than a guaranteed minimum operating time, and that service life and MTBF are different concepts. See Bel: Reliability Considerations for Power Supplies.

Keep three fields in your comparison: the reliability figure and its basis, the expected service life under your application conditions, and the written warranty terms. Ask for each separately. Do not turn an MTBF number expressed in hours into a promise of calendar years, or assume it establishes a replacement entitlement.

Request the basis before ranking the numbers

For each quotation, request the exact model and revision, the method used to produce the reliability figure, the stated operating conditions, and whether the evidence is a prediction, test result or field observation. Ask the supplier to identify the supporting document and its revision. If the basis is missing, mark the entry as not yet comparable instead of giving the largest number the highest score.

A practical review sheet can use these columns: supplier/model, quoted metric, calculation or evidence method, input/load/temperature conditions, document reference, unanswered questions and engineering decision. Keep the original supplier statement attached so a shortened spreadsheet label does not change its meaning.

Send the operating profile that matters to your product

XP Power describes how electrolytic-capacitor lifetime depends on component temperature and other operating stresses, and why the installation and equipment usage profile need consideration. Its technical article is a reference for the principle, not proof of the lifetime of a Voltivo product: Electrolytic Capacitor Lifetime in Power Supplies.

Give the supplier a project-specific brief rather than asking whether the supply is long-life. Include expected powered hours per day, normal and peak loads, periods of idle operation, local ambient conditions, installation space and cooling arrangement. State the intended years of equipment use and whether maintenance or replacement is practical. Ask engineering to review the assumptions behind any lifetime estimate.

For example, a proposed comparison between a continuously operated unit in an enclosure and an intermittently used desktop unit should start with two separate application profiles. This is a planning example, not a customer case or a calculated lifetime claim.

Turn unresolved assumptions into sample-review actions

Ask the supplier which application conditions still require validation and what evidence can be provided for the proposed configuration. Assign an owner to each open item before sample approval. A short functional sample check should not be recorded as evidence of years of field life.

Use the idle and wake-up checklist to describe operating states, and tie the agreed evidence to the approved sample and revision record. If the enclosure, cooling or load profile changes later, ask whether the previous assessment remains applicable.

Confirm support terms independently

Request the proposed warranty duration, when it starts, exclusions, claim documentation, return process and responsibility for shipping costs in writing. Separately discuss replacement availability and notification of product changes. Treat these as questions for the quotation, not services that are automatically included.

A useful RFQ sentence is: Please identify the reliability evidence and its assumptions for the quoted model, comment on our attached operating profile, list any remaining validation requirements, and quote warranty and replacement terms separately.

When contacting Voltivo Power, send your required output, installation conditions, operating schedule, target service period and estimated quantities. Request configuration-specific evidence and commercial terms; this guide assigns no MTBF, service-life or warranty rating to catalog products.