PSU APW3-12-1600-B2 can be used on any version of S4 with some may require cable modifications with the breakout board.
1 string attached with the PSU APW3-12-1600-B2 is you must have 208V or higher. (205v or higher) to be able to use it.
If you have to use 110v, depends on the condition of your PSU, centers in Denver, Ukraine or Serbia may able to repair it for you. If it still powers on and gives you some ERROR LED Status.
Support@bitmain.zendesk.com is the route to request servicing your original S4 PSU if it is not completely dead yet. If the fan won't power on, or no LED light comes on, then it is not serviceable.
Unfortunately at the moment, S4 PSU is not in stock. Time to time, the centers in USA/Serbia/Ukraine may have those in stock so please keep checking with the supports
OK so I sent my S4 PSU to Serbia for fixing came back fixed and worked for about 10 days then same thing. Machine off with ERROR LED status.
Is it a reset that can be done easily - as it costs a small fortune to send to Serbia from UK. If how? Looks fine inside

Re the PSU APW3-12-1600-B2 I notice in the pdf manual it offers 2 types of wiring Type 1 : old type with M4 ring connectors and Type 2 PCIe type
Is this provided? - if not what did you mean by
cable modifications with breakout board. Is it as simple as unscrewing/unbolting the PCI cables from the position shown in the image showing the cables and replacing with the original cables from the old PSU.