Yes, you will and I would recommend some simple ones and maybe another on with USB outlets. The power over there is 220 V at 50 Hz. almost all phone and camera power adapters can handle this just fine, if you want to be sure, just check that they list 110 volt to 220 volt inputs which is written in small letters on the adapter.
Keep in mind that you will not be able to use anything high-power like a blow dryer or a curling iron unless it is made for Europe. The alternative option for curling irons is to get one that charges using a USB connection. There are plenty on Amazon, just search for cordless curling irons. As for blow dryers, most hotels have them.
Greece has both type C and type F outlets, the adapters you will need look like the ones below. There are tons on Amazon, but make sure you pick at least one up before the trip.
Type C, F and G
VINTAR International Plug Adapter $25
This set will cover all of Europe and has a standard US outlet with one USB outlet, two USBC outlets, and two US-style outlets delivering 230 volts.
https://www.amazon.com/European-VINTAR-International-American-Attachments/dp/B0BRSQR7Y6
Type C,E and F
2 Pack European Travel Adapter Plug for European Outlets $8
This basic set will cover all of Greece, just keep in mind that you can only plug in 1 device into each.
https://www.amazon.com/Pack-European-Travel-Adapter-Outlets/dp/B071GC3G9G
Power Banks
It is wise to bring along a couple of fully charged power banks. I try to bring one that I can carry during the day in case my phone dies, especially since I rely on Google Maps to get around and you may need your phone to show pre-bought virtual tickets.
