Sizing the output for your rail
The LM317D2T-TR delivers up to 1.5 A continuous output from an adjustable 1.2 V to 37 V range, with a 40 V maximum input. That 1.5 A ceiling is the hard limit for your load budget — if your downstream circuitry pulls 1.2 A nominal, you have 300 mA of headroom before the over-current protection engages, but the thermal rise in the D²PAK package at that current and dropout voltage needs a copper pour on the tab pad to keep junction temperature below the 125 °C max.
Ripple rejection at line frequency
PSRR is specified at 80 dB to 65 dB at 120 Hz — the range reflects the dependence on output voltage setting and load current. At the high end, 80 dB attenuation means a 1 Vpp ripple on the input becomes roughly 0.1 mVpp at the output, which is relevant for analog supplies feeding op-amps or ADCs that run off the same rectified rail.
Package and reflow reality
The D²PAK (TO-263-3) is a surface-mount package with a large exposed tab on the bottom. The tab is the thermal path and the output connection — your PCB footprint must include a thermal pad with vias to inner copper planes.