The original IEEE 802.3af-2003 PoE (Power over Ethernet) standard provides up to 15.4 W of DC power (minimum 44 V DC and 350 mA) on each port. Only 12.95 W is assured to be available at the powered device as some power dissipates in the cable. The updated IEEE 802.3at-2009 PoE standard also known as PoE+ or PoE plus, provides up to 25.5 W of power for Type 2 devices. The 2009 standard prohibits a powered device from using all four pairs for power. Both of these standards have since been incorporated into the IEEE 802.3-2012 publication.
Looking at ways of increasing the amount of power transmitted, IEEE has defined IEEE 802.3bt 4PPoE in September 2018. The standard introduces two additional power types: up to 55 W (Type 3) and up to 90-100 W (Type 4). Each pair of twisted pairs needs to handle a current of up to 600 mA (Type 3) or 960 mA (Type 4).
Single-pair Power over Ethernet (SPoE) is also known as Power over Data Lines (PoDL) and defined by the IEEE 802.3bu-2016 amendment. With single-pair Ethernet, power is transmitted in parallel to the data and 10 power classes are defined, ranging from 0.5 to 50 W (at PD).