What brand devices?

If you have Apple iDevices AND Apple brand chargers, the charge time should be exactly the same regardless of wall outlet voltage.

That said, Apple makes different capacity chargers. The stock iPhone and iPad MINI chargers are 5 watt maximum output rated.

The Apple charger sold with the full size iPads is rated at 10 watts or 12 watts (there are two variations).

The charging cable also matters. If the cable is internally degraded (excesse flexing, well used) then it can impede charging. Non-MFi cables can affect charging.

A full size iPad that is being charged using a iPhone charger (5 watts) will charge slowly. If the iPad screen is on then it will charge even slower.

If while traveling you are using the device more and the battery level is lower than you normally allow at home, then the charge times will be longer. If the device is hot when plugged in, it will not start actual charging until the internal battery cools down.

Travel tip when staying in a hotel. Sometimes the wall outlet turns off when you turn off the lights. I have had this happen more than once where I plug it in, see it is charging, then turn off the lights to sleep. In the morning, the device is not charged!