Czech Republic uses 230V at 50Hz as its standard household electrical supply. If you're moving appliances between Czech Republic and North America (120V/60Hz), both voltage and frequency are worth checking before you plug anything in.
What to watch for: Czech Republic runs on 50Hz, which does not match the 60Hz standard used in the United States and Canada. A plain step-down or step-up transformer only changes voltage — it does nothing about frequency. For appliances with motors, compressors, or timing circuits (refrigerators, washers and dryers, stand mixers, some stoves, and virtually all microwaves), running them at the wrong frequency can cause them to run at the wrong speed, overheat, or simply fail to operate. A dedicated voltage and frequency converter is what actually solves this — see why frequency matters for the technical reason a transformer alone can't fix it.
Since Czech Republic runs at 230V, a US-spec 120V appliance needs its voltage stepped down before it can be used safely there — and a local 230V appliance needs its voltage stepped up to run on North American 120V power.
A plug adapter only changes the physical shape of the plug — it doesn't change voltage or frequency at all. If the appliance isn't rated for Czech Republic's 230V/50Hz supply, a plug adapter alone can damage it.
No — check the rating label on the back or bottom of each appliance. Many modern electronics (phone chargers, laptops) are dual-voltage and frequency-tolerant. Motor-driven and timing-based appliances are the ones that need real conversion.