The Krueger unit isn’t a PSW inverter where the other one is although that may nor matter to me. The Sunshine Solar unit has 2x + and 2 x - battery cables. I have read documentation for both but still not sure if you can draw 2Kw from a single socket or if these are both in fact two 1Kw units in a single case. Is there a way to tell?
I don't know for sure but I would be very surprised if the dual sockets on any non-specialist inverter are not simply 2 sockets wired in parallel, no different to a domestic twin socket.
Having a pair of DC supply cables instead of one is fairly common with inverters. It is often cheaper and easier to use say 2 x 25mm cable then a single 50mm cable. It doesn't say what size the cables are, but they look like either 25mm (most likely) or 16mm.
Theoretically a 4000W Inverter could be drawing 333A at 12V and that could demand a cable size of 100mm2, but you would never use a cable that size. As an example, the Victron Multiplus 12/3000 (2400W normal, 6000W peak) specifies 2 x 50mm cable, or 2 x 70mm cable if over 5M long. A 100mm cable would be just too unwieldy to use. I have a much shorter run than 5M and use just one cable. When I used a 50mm cable I found it got relatively warm when pulling over 200A for any time, but when I changed it to 70mm cable it stayed cool.
I wouldn't be swayed by the saving from the "before" price of £479 though
