The verdict

Plex
Nvidia Quadro T400 transcodes more streams (~24 vs ~18).
Local AI
Nvidia Quadro P2000 has more VRAM (5GB vs 2GB) - up to ~7B (Q3-Q4).
Fit
Nvidia Quadro T400 is easier to add to a mini-PC (low-profile PCIe).

Which wins for each job

Job Nvidia Quadro P2000 Nvidia Quadro T400
Plex transcode ~18 streams ~24 streams win
Frigate NVR ~25 cameras ~25 cameras
Local LLM 5GB VRAM win 2GB VRAM
Fits a mini-PC full-size PCIe, DIY build low-profile PCIe win

Approximate - capacity estimates from curated specs, the same logic as the recommender. Verify against your exact setup. Prices move; check the retailer.

Full specs

Spec Nvidia Quadro P2000 Nvidia Quadro T400
Price (list) $150 $130
Type gpu gpu
Interface pcie pcie
Transcode H.264/HEVC (NVENC Pascal) H.264/HEVC (NVENC Turing)
Frigate detector TensorRT TensorRT
TOPS - -
VRAM (GB) 5 2
Low profile no yes
GPU sharing vgpu (unlock) vgpu (unlock)
Power (W) 75 30