Formal:
* Sufficient: This is a very common and general term.
* Adequate: This implies that something is "good enough," but not necessarily excellent.
* Suitable: This suggests that something is appropriate for the specific purpose.
* Competent: This emphasizes the ability to do something effectively.
* Effective: This focuses on the outcome or result of the action.
Informal:
* Up to the task: This is a more colloquial way of saying "capable."
* Fit for the job: This implies that something is the right tool for the task.
* Good enough: This is a casual way of saying "sufficient."
The best adjective to use will depend on the specific context and the desired tone.