The verdict

Plex
Nvidia Quadro P400 transcodes video; Google Coral USB Accelerator is detection-only (no transcode).
Frigate
Nvidia Quadro P400 handles more cameras (~25 vs ~5).
Local AI
Nvidia Quadro P400 has 2GB VRAM (too small for useful LLMs); the other has none - not for LLMs.
Fit
Google Coral USB Accelerator is easier to add to a mini-PC (USB, fits any box).

Which wins for each job

Job Google Coral USB Accelerator Nvidia Quadro P400
Plex transcode none ~18 streams win
Frigate NVR ~5 cameras ~25 cameras win
Local LLM none 2GB VRAM win
Fits a mini-PC USB, fits any box win low-profile PCIe

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 Google Coral USB Accelerator Nvidia Quadro P400
Price (list) $60 $60
Type tpu gpu
Interface usb pcie
Transcode - H.264/HEVC (NVENC Pascal)
Frigate detector EdgeTPU (native) TensorRT
TOPS 4 -
VRAM (GB) - 2
Low profile no yes
GPU sharing - vgpu (unlock)
Power (W) 2 30