@chr0m4t1c 

The S210 is adaptable.

In fact, your line composition is:

Live--Lin (S210)-Lout(S210)--Load--Neutral

TP-Link's website has S210 installation instructions and videos that may be helpful to you.

  @Akitsuki

Ah, so my "neutral" will actually be a switched live with the loop in the ceiling rose and should have been marked with some red tape to indicate that it will be live when the switch is on, but hasn't been so that's why I was confused.

Thanks.

  @chr0m4t1c 

This switch seems powered by battery instead of the neutral wire, so you just need to connect the live and load wires and cap the neutral. 

  @GabrielMitch 

I think you have misunderstood my setup.

I only have three wires, one of which is an earth/ground and is attached to the metal pattress box in the wall.

The other two are red (live) and black (should be neutral).  If I cap the black wire there would be no load wire and hence no circuit.

My dumb switch sits between the red and the black wires, so the black must actually be a switched live (load), but has not been marked with any red tape to indicate that.

My confusion came from my old wiring and the specific advice from Tapo to cap off any neutral wires, when I can just do a 1:1 replacement with my current dumb switch.  Akitsuki pointed out what the circuit must actually look like and helped me get it clear in my head.

  @chr0m4t1c 

Oh right, yes, i did not picture it really well in my head. Probably that's why I can't be an electrician.

  @chr0m4t1c 

did you get yours set up. I have the same setup with wires currently. Where did you put yours into the Tapo light switch? I have a red wire currently in the com slot and a black one in the l1 slot 

  @LukeBorman Yes, that's the same setup I used and mine is working fine.

Basically the black wire is what's called a switched live in that it is live when the switch is on and technically neutral when the switch is off.  The actual connection to your neutral loop will be at the light fitting.

The wire that connects the switch to the light fitting is supposed to be marked by having a piece of red electrician's tape wrapped around it to indicate that it will be live when the power is on, but that's a more recent standard so older houses/wiring probably don't have it.

Wiring like this is perfect normal and means only running a single cable from the fitting to the switch, but I'd forgotten that mine might not be marked properly.  Akisuki pointed out what the circuit actually looks like.

  @chr0m4t1c 

so I have three wires in my switch. I think one is black and one is blue and the last is the green/yellow. 
 

i assume the black is the load and the blue is the live?

bt the ground. Where they go in the tapo switch?

  @Lethaldesi 

Lethaldesi wrote

  @chr0m4t1c 

 

so I have three wires in my switch. I think one is black and one is blue and the last is the green/yellow. 
 

i assume the black is the load and the blue is the live?

bt the ground. Where they go in the tapo switch?

That's an odd combination of colours, black+red is the "old" neutral+live combo and blue+brown is the new neutral+live combo, so I can't say for sure which is your live on that setup.

You really need someone to test the wires to find out which one is live if you don't know.