Does 802.3bt PoE++ work with 2-pair power or does it require 4-pair power?

802.3bt always requires four pairs for power >= 40W (class 5+) and **does not support powering over two pairs.**Powering 2-pair devices using 802.3bt will only when powering devices with up to 30W (i.e. in “802.3at backwards-compatible” mode).

For reference see this whitepaper by the Ethernet Alliance.