Don't use a password generator website. Thousands of Bitcoins have been stolen this way. Even if you use if offline, it is HIGHLY LIKELY to give you intentionally or unintentionally predictable output.
If the random password generator is offline, there is nothing bad to use it, but I consider it stressful than to randomly input different characters on my keyboard, but that does not mean it is not safe, nothing connected it online, but use the recommended ones. If connected online, then it is not advisable as well do not know what as running underground to steal the password online immediately after creating it.