Obsolete but still spec'd — the 1.5KE120C-B sourcing reality
It clamps at 173.25 V max with a 9.2 A peak pulse current capacity, and the reverse standoff voltage is 102 V.
What the ratings mean for the protection circuit
The 173.25 V clamping voltage at 9.2 A is the worst-case voltage the protected load sees during a surge; if your downstream components have a higher absolute maximum rating, the TVS absorbs the energy before they do. The DO-201AA / DO-27 axial-lead package is through-hole — it stands off the board and dissipates heat through the leads into the PCB copper.
Sourcing an obsolete TVS — what to expect
Because Littelfuse has discontinued the 1.5KE120C-B, new inventory comes from independent surplus or broker channels. Each lot is verified for authenticity and tested to the original datasheet limits before it ships. No official pin-compatible successor is listed by Littelfuse; the closest functional match would be another 1500 W bidirectional TVS in a DO-201 package with a 102 V standoff, but the clamping voltage and pulse current must be cross-checked against the original spec.