Does the A2B bus carry power?
Yes! Each locally-powered transceiver can supply up to 300mA (up to 2.7W) over the A2B bus to the next downstream slave. If that bus-powered slave doesn't require the full budget, it can then supply the remaining power to the next slave. This power budget then resets to 300mA at the next locally-powered slave in the system.
Maikel is correct in confirming that the AD2429(W) can deliver 100mA of current over the A2B bus, but I need to clarify that the spec does NOT apply to the AD2420(W). Since the AD2420(W) transceiver is a last-in-line slave device, it does not have the ability to provide downstream power, so we will need to correct this in the data sheet.
Specifically, AD2420(W) must be removed from the "Conditions" column of the Electrical Characteristics table for the I(VSSN) specification. Similarly, the related 300mA full-featured I(VSSN) specification does not apply to the AD2426(W) transceiver, which we will also address.