How much power is the Pi port capable of delivering, or are you sending additional power to the PCIe adapter from somewhere else?
What SmartNIC are you using? Most SmartNICs that I'm aware of suck a decent amount of power, many more require significant external airflow. Are you using the Mikrotik active cooled one? https://mikrotik.com/product/ccr2004_1g_2xs_pcie
The Pi port can deliver 5 or 10W max at 5V IIRC. So I'm not using it :D
The 12V comes from an external power supply through a barrel jack, from which I also derive the 3.3V rail. The Pi provides no power whatsoever. I should publish the design files somewhere.
As for the NIC, it's a Netronome Agilio-CX which is fully programmable using eBPF and such.
What SmartNIC are you using? Most SmartNICs that I'm aware of suck a decent amount of power, many more require significant external airflow. Are you using the Mikrotik active cooled one? https://mikrotik.com/product/ccr2004_1g_2xs_pcie