h3ndrik , 1 month ago (edited 1 month ago)

Most mainboards in full-sized PCs aren't optimized for power efficiency. But there are some (few) efficient mainboards and PSUs available.

The german c't magazine publishes guides to build efficient home-servers or workstations every other year. But that's well above your budget: https://www.heise.de/ratgeber/Bauvorschlag-fuer-einen-sparsamen-Heimserver-aus-c-t-3-2024-9587594.html
(400€ new, 17W idle)

The Lenovo seems to draw around 45 Watts on idle. You could go well below 20 Watts if you wanted.

I'd say for most power efficiency along an extremely low budget, you want an old laptop as a home server, or a mini pc like an Intel NUC. But you might want to refine your requirements... What do you need that thing for? How many SATA-Ports etc do you need? Are you more willing to compromise on price or power efficiency?