Do you have to convert that -48volt to 12volt.
Can't you just use a regular 12volt supply, powered from one mains phase and neutral.
If not, try that trick that @PerryBebbington mentioned in post#6.
Leo..
It can.
Things will get >= warm.
My suggestion is the addition of a fast-blow fuse between it and the 48V.
You can't learn everything from simulations.
Converting negative 48volt to positive 12volt is unusual, so you can't find off the shelf parts for that. Maybe OP needs to tell us what he is using this old supply for. Maybe it's more logical to convert it to a positive (negative ground) supply.
Leo..
Thats very interesting , what is the input AC voltage of the 'wall wart' ?
I tried it on a 100 - 240Vac / 12V 1A input but no output , not even on 52V DC as input.
I live in the UK, so nominally 230VAC.
This is what I consider to be experimental things to try, not something guaranteed to work. All wall warts are not created equal, some will work, some not. I got lucky I suppose, the first one I tried worked. How many have you tried? I don't imagine they will all work on 50VDC.
Thanks for the reply.
I tried 3 different once not one worked but 2 worked when I change the start resistors to 22k.
But I dont get 1A as rated , they light up a 12V globe 12W then pulse on , off ,on , off.
I will do more tests maybe I will get 400 to 500mA.
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Good 
This is what I love about electronics! You can experiment with this stuff easily and do things, sometimes things other people, some of whom claim to be 'experts', say cannot possibly work.
Mine worked without changing anything. The load I put on the output was quite a bit below the rated output. It doesn't surprise me that when supplying at a lower voltage than rated the thing doesn't give the rated current.
If we could get to those primary windings.
..it might hurt..
My ego when going the extra mile and the result is the same or worse.
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