I have both 2B and 3B modems here along with a black and a white power supply. Both are 12V DC and the older black a 700mA unit whereas the white is rated at 1.0 A
The two modems look identical inside, and there appear to be no component changes - there is some extra silicon "glue" to hold some components stable and the heatsink square but nothing else.
The quiescent current - no network or DSL connection. 490 - 500mA
Connected the network and DSL, there is a small peak before settling back to 490 - 500 mA
During a full download of a 200MB file (40 seconds) the current increase to around 520 mA
With an upload there is a similar increase and if the upload and download are running at the same time the current peak at 550 mA
The 2B took a few mA less than the 3B but that could be due to tolerances. The current from the black power supply was also marginally less.
So, a 700 mA supply should be capable of supplying a modem running 17c profile and a 40/10 connection.
However, when 80/20 Mbps is introduced, I would expect there to be an increase in power to 600mA (or thereabouts) and if BT ever bring in 30MHz profiles then potentially another 50-100 mA which will be on the limit of the supply. The extra power will be required for the processing in the software modem and driving the upstream.
Also, at turn on teh peak current was in excess of 600mA (meter limit for fine measurments) and around 0.8A (higher rated range) which should not be a problem for even the black power supply for s short burst.
I also measured the DC voltages:
Black: offload 13.3v loaded 13.1v and was not wonderfully stable.
White: offload 12.2v loaded 12.15v
Not too much of an issue but there will be a need to dissipate an additional 600mW of heat.
Overall conclusion from a short 2 unit test is that the black PSU will cope but will towards its limit where as the white is well within design parameters.
Do I think they should be replaced? Yes, to improve long term reliability of the PSU and potentially modem.
M H C
taurus excreta cerebrum vincit