Matt:

You can't "step down" frequency--only voltage.

If you want to run a device from this socket, most items would probably be ok.

For example, if you want to plug in your cell-phone charger: the charger does step-down the voltage to something between 3 and 12 volts, depending on model. There will be diodes in the charger to change the AC to DC, and a filter--composed of capacitors, resistors, and sometimes coils, to smooth-out the peaks and valleys of the former AC current.

This capacitor-resistor-coil circuit is optimized for 60 HZ. However, the slightly "wavey" DC that would result from such a power supply with 400HZ should be OK for most phones and/or laptops, as the phone or laptop has additional Cap-res-coil circuits, and the charging of batteries doesn't really depend upon a stable frequency.

Of note: AC motors don't work with incorrect frequencies. Electric razors, and vacuum cleaners, margarita blenders (probably aren't taking these on your trips) should NOT be used with 400 HZ current!

Bottom line for common electronics: plug it in. If it works fine, use it. If it acts strange, then don't--but it shouldn't damage it.