tb wrote:
The charger cord for my AT&T's DSL modem (2Wire 2701HG-B) died, so I
purchased a new one online at Amazon.com.

The only difference between the original cord and the new one is that
the old one output was 5.1V @ 2.2A, whereas the new one is 5V @ 2A.

The modem seems to work ok with the new cord. But, because I am not a
techie, I don't know if such a difference in V and A could damage my
DSL modem in the long run.

What do the experts have to say?

According to this, one person here found a load of 1.2A. And that value
is less than the 2.2A or 2.0A maximums allowed on your two powering
solutions.

http://www.dslreports.com/forum/r228...Supply-Problem

The IC tolerance should be at least 5%. If there really is something
running off +5V in there, it should at least tolerate 5.25V on the high
side, or 4.75V in the low side.

They could be attempting to compensate for voltage drop in the cord
under load, but that seems pretty goofy.

There's not much to see inside. It does have a power converter
in the lower left, but may also be using the input power in
raw form, elsewhere in the unit.

https://wikidevi.com/w/images/1/1d/2..._board_top.jpg

I don't see a reason to panic at this point. The 5.1V is clever,
but also non-standard, and it's surprising anyone in China
is sourcing an adapter actually set to 5.1V. But the objective
is, to compensate for the ohmic drop. 5.1V minus (1.2A times 0.008 ohms)
gives 5.0V at the plug. That's the idea. The cable has resistance,
and the regulation point is inside the adapter. The adapter doesn't
know what the voltage is at the plug, and maintains the voltage
at a reference point inside the adapter. It doesn't use remote
sense, like the 3.3V rail on an ATX supply does. (If you check
your ATX supply main power cable inside the PC, one of the
pins has two wires leading to the same pin, and that's the
remote sense on the 3.3V rail only.) Wall adapters, and a lot
of power sources, don't bother with remote sense as a feature.
Boosting the output voltage like that, is a poor mans way
to "fix" the drop in the cable.

Paul