PED's don't care, the chargers/power supplies don't care, it is cleaner power, anyways the input is AC the output is DC.
Just plug your computer, tablet, phone etc. into the 400hz outlet, been doing it for years and never fried anything.
Both statements are basically true for modern gear.
An old tech "wall wart" power supply "might" run a bit warm if it has a (iron core) stepdown transformer directly connected to the line due to higher losses at 400Hz.
Almost all modern wall warts use a switching converter that runs from rectified DC, full wave bridge + fillter capacitor.
This allows the stepdown transformer to be mutch smaller (aka cheaper) since the frequency is >> 100Khz.
If anything they should run cooler since the input filter capacitors will be more effective at 400Hz than 50/60Hz.
On the other hand many (most?) are not tested/certified by the manufacture to run on other than 50/60Hz.
The real restriction is whether the relevant authorities recognize the unit as safe/suitable, hence the existence of kludges such as invertors to provide 60Hz.
When/if certification is required is totally outside my area of expertise.
BTW: Any equipment with a normal line cord (not a wall wart/DC supply) may have problems if fans or other motors are run directly from the AC power.
This is not commonly found in the consumer computer world but is sometimes seen in industrial gear or older consumer products such as tape recorders.