You asked about mini-PCs, which I don't have, however just for comparison I can say I have ODROID-XU4 + cubietruck here running and only drawing about 2W total between both of them.

I wouldn't necessarily recommend those (especially the cubietruck) these days, but there are lots of Single Board Computers (SBC) out there besides RPi.[0]

[0] https://www.armbian.com/download/