I want to buy an external ssd for photo and files storage. I see interesting offers, but most external ssd's with good reviews are encrypted. As I understand, encryption software works on Mac and Windows.
I was wondering if such hard drives can be used under Ubuntu? I don't really care about encryption, since I want to use the drive for storage and everything should be accessible right away.
If I buy an encrypted SSD, can I format it in ubuntu and turn it into a regular hard drive?
The encryption you are talking about is a hardware feature of the SSD where there is an included encryption module. Using a drive with this feature has no impact on your ability to install Ubuntu on the SSD, with or without encryption.
Here is an example of how one manufacturer (Crucial) implements hardware encryption on their SSDs: The Benefits of a Self-encrypting Drive.