[dingaling]

802.3at specifies max 30W at the output port at 600mA so in theory you could shunt that to 5V and get about 5A after losses. Enough to spin up a 3.5" SATA.

But most consumer retail PoE switches are only .3af compliant which give 15W minus transmission losses.

[conk]

802.3bt can provide higher power, easily enough to run a few HDDs but there are few switches on the market that offer 802.3bt. Almost nothing available for the residential/consumer space.