What a 1500W clamp means on a 26V rail
The 1.5SMBJ26CA: With a 26 V reverse standoff voltage, it clamps a transient to 42.1 V maximum at 35.7 A peak pulse current — that 42.1 V ceiling is the voltage the downstream silicon sees, so the 26 V rail's downstream devices need at least that much breakdown margin. The breakdown starts at 28.9 V minimum, meaning the diode stays off below that and only conducts during the transient — no leakage penalty under normal 26 V operation.
Automotive grade and the AEC-Q101 stamp
The DO-214AA (SMB) surface-mount package is standard for this power class; the 1500 W rating assumes a good copper-land layout on the PCB to sink the heat pulse.