General:
* Supportive - this is the most straightforward and common choice.
* Helpful
* Assisting
* Beneficial
* Aidful
* Encouraging
* Comforting
Specific:
* Structural - for physical support
* Financial - for monetary support
* Emotional - for emotional support
* Moral - for ethical support
* Practical - for tangible support
* Technical - for specialized support
Figurative:
* Unyielding
* Firm
* Strong
* Solid
* Reliable
* Dependable
The best adjective to use will depend on the specific situation and the type of support you are referring to.