Type 1. A capacity flow for high-energy systems. - Warp Nacelles, Defense systems, Field generators, etc

Type 2. A capacity flow for experimental devices. - Science, Engineering and Medical labs, Holodecks, etc.

Type 3. A capacity flow for low-power input applications. - Computer core and all subsystems, lights, PADDs, etc.

Both MARA (warp) engines, and Fusion (impulse) engines feed the EPS Taps.  Aboard starships, the Warp Core generally feeds the warp nacelles, shields, and weapon systems (phasers), and the Fusion engines feed various 'departmental' needs.  All of course can be re-assigned by the OPS officer as needed.

When both MARA and Fusion engines are down backup generators and/or solar collectors are used to maintain all ship's power usage.  But if neither systems are repaired, the generators eventually run out of energy and the ship/base can be lost.  If repaired, the EPS will promptly re-charge the backup generators.