What the 500 V / 12 A rating means for your power stage
The STP13NM50N: Its 500 V drain-source breakdown voltage and 12 A continuous drain current target offline power supplies, power-factor-correction (PFC) stages, and 400 VDC bus converters where the TO-220 package can be bolted to a heatsink. At 12 A, expect I²R losses around 46 W — well within the 100 W package dissipation limit at a 25°C case temperature, but derating is required as the case heats up.
Sourcing an obsolete part — what to expect
STMicroelectronics lists the STP13NM50N as Obsolete. The MDmesh™ II generation has been superseded by later MDmesh series, but pin-compatible alternatives exist across ST's own portfolio and from competitors — verify the gate-drive voltage and switching speed match your design.
The TO-220-3 through-hole package is a standard power-device footprint. The tab is the drain terminal, so the heatsink must be electrically isolated or the system must tolerate a live tab.