9V rail clamp in a DO-214AC footprint
Its reverse standoff voltage is 9V, and the breakdown voltage minimum is 10V, so the part remains transparent below 9V and starts conducting at 10V to shunt the surge. Rated for 500W peak pulse power at the 10/1000µs waveform, it can handle a peak pulse current of 32.6A before the clamping voltage reaches 15.4V max. That clamping ceiling is what the downstream circuitry must survive — if your 9V rail has a 16V absolute-maximum input on the regulator, this part buys you a solid margin.
The part is unidirectional with a single Zener channel, so it clamps only positive transients relative to ground. For AC or bidirectional protection, you would need two devices back-to-back or a dedicated bidirectional TVS.
Microchip lists the SMAJ9.0AE3/TR13 as Active, meaning no end-of-life notice is in effect. The suffix indicates RoHS compliance and tin-lead (SnPb) termination finish — verify your assembly's solder alloy compatibility if moving to lead-free-only processes.