[Plugin: Get Custom Field Values] About sidebar widget

Yes, the widget only retrieves a custom field according to a specific field/key. That field can appear multiple times for a post, or in multiple posts. It currently does not support retrieving multiple custom field keys in a single widget or request.

Could you provide an example use case where you want to get the values for multiple custom field keys in a single widget?

Well, in my case I use custom field to show information about songs, like author, year etc.
I’v always used this same plugin to display information within the post page, now I wanted to try display them in a sidebar.

Unfortunately the widget does not currently facilitate being as freeform with the output of multiple custom fields for a post as is possible when using the template tags within template files (as that’s what you seem to be saying you currently do).

If you’re already using the template tags within a post/page template, you can also use them in the sidebar. There are variations of get_custom(), such as get_current_custom() that work in the sidebar template.

But I do understand your use case though. I have plans for additional functionality that will make doing what you want to do quite easy. No time estimate on when it’ll be ready though. Until then it’s either the template tag approach, or multiple widgets.