500W peak pulse, 150V standoff – what it protects
The SA150A: This puts it squarely on a 150V DC rail, typical in telecom rectifiers or industrial power supplies where a single surge event can exceed the downstream regulator's abs-max.
Obsolete – sourcing through surplus channels
A board spin to a current TVS family (e.g., onsemi's 1.5KE series in DO-201) may be the longer-term migration path.
DO-15 axial – footprint and fit
Housed in a DO-204AC (DO-15) axial-lead package, the SA150A is a through-hole device — the leads insert into plated through-holes on the PCB and are soldered on the opposite side. The axial form factor is common in power-entry and telecom protection stages where the diode sits in series with the protected rail or across the input terminals.