The power supply of many oscilloscopes and other test equipment from different manufactures are commonly rated for 400 Hz operation. For example, Tektronics MDO3000 is rated to work at 400 Hz at 115 VAC. Rigol MSO7000 is rated at 100-240 VAC, 45 Hz-440 Hz.
I'm aware that 400 Hz power supply is widely-used in aerospace, and I heard some military and industrial installations also use 400 Hz, mainly to reduce the weight of the transformer. But I didn't find any specific case online.
What are some specific scenarios when users are expected to connect the oscilloscope to a 400 Hz power supply? Using an oscilloscope on a flying aircraft sounds unplausible. Most laboratories, industrial or otherwise are likely supplied with 50/60 Hz AC to power all equipment. The only possibly I can think of is field-engineers doing tech support. But even then, I believe it's more common to use a portable, battery-powered oscilloscope.
Does anyone who has an industrial background can explain: Is that really difficult or inconvenient to find a standard mains-frequency power in some factories to make it justified for most oscilloscope manufacturers to rate their scope for 400 Hz operation?