1500 W peak pulse in a DO-214AB footprint
The 1.5SMC150A-E3/57T: The 7.2 A peak pulse current rating at the 10/1000 µs waveform is the current the device can handle during a surge event — the clamping voltage of 207 V is the voltage the load sees during that event, so the downstream circuit must tolerate that peak.
Breakdown and standoff — the protection window
Minimum breakdown voltage is 143 V; below that the diode is off and the protected rail sees only leakage. The standoff voltage of 128 V is the maximum continuous DC voltage the device can sit across without conducting — a 120 VDC bus is well within that margin.