What the 1500 W peak pulse rating means for your rail
The 1.5KE200AT/R: The 274 V maximum clamping voltage at 5.5 A peak pulse current (10/1000 µs waveform) means a surge on a 170 V DC bus or a 120 V AC rectified rail gets clipped before it reaches downstream silicon. The 190 V minimum breakdown voltage gives a 19 V margin above the standoff — enough to ride through normal ripple without conducting. This is a unidirectional device (single channel), so it clamps only one polarity. On a bipolar line you would need two back-to-back or a bidirectional part.
The DO-201AA (DO-27) axial leaded package is a through-hole form factor — the leads are 0.037-inch diameter tin-plated copper. The body is 0.210-inch diameter, 0.410-inch long. The axial leads mean it can be mounted standing upright or flat against the board; the thermal path is through the leads into the solder joints and PCB copper. No exposed pad — all heat flows through the leads. The Tape & Reel packaging is for automated insertion.
EIC lists the 1.5KE200AT/R as Active.