All devices are rated in both voltage and amperage. The reason the voltage is not typically listed is because the market defines the voltage available and the plug on the device is what tells you the device’s voltage rating, if nowhere else. It’s still important to tell you if it requires an adapter, ignoring the part where the average consumer isn’t going to try to wire a NEMA 5-15 (regular north American plug) to a 12v barrel plug.

This next part is not me trying to be a know-it-all, but to dispel an incredibly dangerous misconception. Amperage is not necessarily what kills you. That is a myth, and a dangerous one at that. Amperage is what causes burns, including internal burns, and is what kills you later at the hospital. Higher voltage is what kills you NOW by finding more paths. If it crosses your heart or brain, it’s probably over. Electricity does not seek the path of least resistance, but rather it travels across each path inversely proportional to the resistance. If you complete a circuit with opposite hands, you’ll probably be safe because your chest cavity of blood vessels will conduct the majority of electricity in paths other than through your heart or brain. AC power and higher voltages increase this risk. Low voltage is not entirely safer, but for most consumer use, “low voltage” is mostly below the breakdown voltage of dry skin, about 30-40v. Wet, and especially sweaty skin will conduct far lower voltages - licking 9v batteries is a normal example, but I’ve also been shocked by a 12v car battery the first time I worked around a side-terminal battery. Opposite forearms, too, so you can bet I took a minute to monitor my pulse. But the Lethal voltages and amperages are in the milli-unit range if they find the correct path. That’s not a high threshold, even with the significantly lower resistance pathways across your chest taking the majority of electricity. And, even if it was just amperage that kills you, you have no control over it because you’ll never know how much resistance you’re creating for the circuit to travel. It’s an unknown variable that’s supposed to be infinitely large but, if you’re getting shocked, it’s something lower than infinity. I household circuits, your drawn amperage will be much lower than the 15a circuit breaker and it won’t trip to save you. That is where GFCI circuits come into play by detecting incorrect electricity paths rather than amperage overload. 15a circuit breakers prevent fires. GFCI prevent death.