Yes, it is generally safe to leave a charger plugged in, even if no device is connected. Modern chargers are designed to operate efficiently and safely, even when they are on without a device being connected.

However, if you are not using the charger or if you are away for an extended period, it might be a good idea to unplug the charger. This saves energy and reduces the risk of any electrical issues, such as short circuits or overheating.

It's also important to note that some chargers can continue to consume a small amount of energy, even when no device is connected. This is often referred to as standby power consumption. If you are concerned about energy savings, you may choose to unplug the charger when it is not in use.