"支持北部联邦者" can be translated into English as "supporters of the Northern Federalists" or, depending on the specific historical context and intended meaning, more contextually appropriate phrases like "advocates for the Northern Federal cause" or "those in favor of the Northern Federal alliance" might be used.
However, if referring specifically to a historical group or movement during a certain period (like the American Civil War era), "supporters of the Northern Federalists" is a straightforward and commonly understandable translation. If the term refers to a more niche or specific group within that broader context, additional context might be needed for a more precise translation.
In most general discussions, "supporters of the Northern Federalists" would be an acceptable and clear translation.