I have been using the AV500 powerline adapters for years without any issue.  I live in South Africa and we are experiencing load shedding from our electricity supplier.  I bought a UPS/inverter to mitigate the loss of internet connection during these power cuts.

I live in a two storey house and I use the powerline adapter to connect to wifi on the ground floor.  My fibre box and router are on the second floor.  

The problem arise when I plug in the UPS to charge.  I lose internet access on the ground floor.  The powerline adapter still recognises that it is part of a network but there is no internet access.  The UPS is plugged into a different wall socket than the fibre box and router.  The aim is not for the UPS to keep the powerline adapters going while the power is off.  It is only meant to keep the fibre box and router online.  All powerline equipment is plugged directly into wall plugs. 

It looks as if the UPS is causing interference when plugged into the wall plug for charging.  It is a simulated sine UPS.

Is this a known issue?  I hope there is someone out there that can shed light on this issue.