Most Postgres clients have issues connecting to Amazon Redshift. The wire protocol is the same so basic interactions (ex: connect via psql and run a SELECT) usually works but things get hairy when you start doing more complicated things or even just querying the data dictionary (the basic information_schema is there but Redshift has it's own tables for it's specific features).

My company[1] makes a database client that runs in your web browser that has explicit support for Redshift (as well as Postgres, MySQL, and more). I encourage you to check it out.

[1]: https://www.jackdb.com/