For your electronics, you will probably just need a converter plug (round to flat) Check the transformers on the chargers, but generally anything from cell phone through laptop will convert anything from 110 through 240.
For other electrics, you’ll need an converter as well as the adapter plug. Be sure to get a heavy duty model if you are going to take something high wattage like a hair dryer.
I don’t know about the Czech Republic, but in Germany the outlets are round and recessed, so depending on the design of the converter, you sometimes have to pair it with an adapter plug to fit into the outlet. The weight of the converter tends then to pull the adapter out of the socket. A roll of electrical tape can help in those situations. You shouldn’t have that problem with the chargers that just use an adapter plug.
“The weight of the converter tends then to pull the adapter out of the socket. A roll of electrical tape can help in those situations. “
Very good advice. However, I found that gaffer’s tape worked better. I purchased a 1 inch wide roll of white glow in the dark tape on Amazon and keep it in my travel bag. It’s far better than duct tape and leaves no residue.