What the clamping ratings mean on the bench
The SMBJ120CA-13: It clamps a 120V nominal rail — the reverse standoff voltage is 120V, breakdown starts at 133V minimum, and the clamp hits 193V maximum at the 3.1A peak pulse current.
Package and field-swap fit
DO-214AA (SMB) surface-mount package, the same footprint as the standard SMB diode. No polarity to get wrong — bidirectional means it lands either way, which is a real help when you are swapping it on a board without a schematic in front of you. General-purpose application classification — no special line-protection gimmicks, just a straightforward clamp diode.