Why do you need a custom military power supply?
Military power supplies are tested against military standards (MIL-STDs) that helps impart trust for purchasers that the device will work when needed and is inherently dependable and robust. The challenge is that many require power supplies for a specific operation and excessive weight is usually undesirable. This means that a custom military power supply is required to meet the performance requirements of the client.
The factors that need to be considered are form, fit, function and cost. You may require mechanical, physical or thermomechanical changes made to the design for a specific operation or platform. Here a prime issue could be the lack of a fan meaning passive cooling technology needs to be used and built around the installation volume of a platform using it. At the expense of cost a custom military power supply can be created with a passive cooling heatsink or utilize a Peltier plate in some niche applications.
Extreme ambient temperatures and peak temperatures can also be a good reason for creating a custom military power supply that offers better direct sun resistance through reflective infrared coatings to the case and optimized internal heat pipes to help get internal heat to the exterior of the device. Testing the new design may require retesting to MIL-STD the entire device increasing the cost extensively. Unfortunately, this cost is passed to the customer which can be a big challenge when it comes to selling the devices and making a profit however the function of the device will be exactly what is required for the client.
Off the Shelf
Off the shelf devices are mass produced to reduce the unit cost to the buyer. They may be designed to be a Jack of all trades compromise and will likely be reflected in the O/I ports and additional options such as a N+1 power management system to revert to a backup and information display on the face plate of the device. From a customer and manufacturers perspective these provide the best bang for the buck and means no additional MIL-STD testing is required as the design remains consistent for approximately a two-year manufacturing and support period. This two-year period is normally so short due to continued changes in components and better efficiencies as well as changes in I/O preferences. Additionally, if a battery is built in and used continually the latest design is a great reminder to users of an older product to buy a new one to ensure they get reliable service.
Light Modified Power Supplies
When the one size fits all approach a light custom MIL power supply may be useful, these are modular and useful where you want to customize up to approximately 20% of the design. This typically means changing I/O ports and reduce power management options to save weight of the device or conversely to add them in. This is a go between in terms of cost and performance as the parts are modular they are easy to incorporate into a design but normally have excessive weight due to the modular nature. They also are not good for custom fitting volumes or platforms due to a consistent case shape used. With these the benefit is reduced cost per unit due to no retesting of the light custom MIL power supply is required.
When considering if you need a custom MIL power supply you should be asking yourself about the form, fit, function and cost of the product and consider if an off the shelf or light modified solution would be much more cost effective with the trade of in terms of how well it matches the ideal solution.