Hi,
In an attempt to tidy up my networking cupboard (and remove three wall-warts), I tried replacing the PSUs for my two HG612 modems and a Netgear 5-port managed switch that sits between them and my router (all require 12V and < 1A) with a 12V/2A barrel connector POE splitter and 3-way adapter cable.
I have two VDSL lines, which both normally report around 83/23 (max attainable), giving me a line sync speed of the full 80/20.
However, when using this POE splitter -
https://www.amazon.co.uk/gp/product/B07TML96C9 - both lines dropped to sync at around 65/16.
I left this installed for a couple of weeks, wondering if it was just a temporary glitch, but no - it stayed the same speed, and I would get frequent (perhaps once or twice a day) reconnections.
Today I tried a different POE splitter -
https://www.amazon.co.uk/gp/product/B08HS4NT13 - and the speeds returned to normal (80/20 line sync)
Putting the other splitter back, and immediately the line speeds dropped again. New POE splitter: back to 80/20.
Reading the reviews of the first splitter, I came across this review from Germany:
"This PoE splitter should supply my Fritzbox 7490 with Ethernet and power, both are supplied by a Unifi switch. The product produces and transmits interference signals via the power grid, so that DSL connections are disrupted. My own DSL connection and that of a neighbor in the low frequency band were so severely disrupted that after several unsuccessful attempts by Deutsche Telekom, the Federal Network Agency was called on the scene and in the end I identified this device as the cause. Device decommissioned, interference eliminated. "
Anyone come across this type of problem before?