Q.There are products that indicate time to failures with MTBF and those that indicate time to failures with MTTF, but what is the difference between the two?

Power Supplies >  Switching Power Supply >  AC-DC Power Supplies/ DC-DC Converters

A. MTBF (Mean Time Between Failures) indicates the average time it takes for a product to become faulty from the time it is first used or from the time it becomes faulty after it has been once recovered.
MTTF (Mean Time To Failure), on the other hand, indicates the time until a product becomes faulty after initial use.
The same calculation methods are used for both, but MTBF is generally used in reference to products that can be repaired and MTTF is generally used in reference to products that cannot be repaired.
We normally use MTBF to represent the reliability of power supply products, but also particularly use MTTF to represent products that are obviously difficult to repair such as compact on-board products.