This is not a technical question, but an ethical one.
If you store passwords, you're responsible for them. Let's assume that someone uses the same password for different services. Now, you have that password. What if their Google account is hacked next week, and then someone uses that to buy good for 100.000 € online. Are you sure, it's not your fault? Maybe, someone has places a trojan on your computer?
You should only store passwords unencrypted, if you're 100% sure that these are not real passwords. Anything else would not be acceptable by means of IT security, and ethics.
Technically, just use a text input for the passwords, and SoSci Survey will store them in the dataset. You could use JavaScript to switch these inputs to the typical password inputs that only show dots instead of what is written.