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How to split single PPPoE connection into two but use one at a time?

I want to split my PPPoE connection into two ethernet cables to connect with two routers, Router A and Router B. But, I will use one router at a time to log in to PPPoE.

The reason is, Router A will run only when electricity goes away and rest of the time Router B will be on and working. I could keep switching the RJ45 connector from one router two another but that’s not a permanent solution. Is there a way to split a single PPPoE connection into two? Will a Ethernet/RJ45 splitter work here?