[quote author="uk03878"]
How do you identifier whether you can get a bipolar supply out of them
[/quote]
Normally a power supply capable of a bipolar output will be described as a 'dual' supply.
+/- terminals probably only indicate that the supply is isolated, i.e. not referenced to ground. There may be a third terminal for ground, so you can connect that to one of the outputs to create +/0 or 0/- supplies, but a single supply can't create a +/0/- from this.
I have a Thurlby Thandar PL series power supply that I'm very happy with. Other manufacturers are likely to offer a very similar range of models:
http://www.tti-test.com/products-tti/psu/pl-series.htm
These are available as single, dual, or triple supplies. Mine is a triple, which has the same two full-featured outputs as the dual, and adds a fixed 5V output for logic.
On the dual (and triple) supplies, the two main outputs are isolated and independent. You have a choice of four ways to use them:
1) Two completely independent supplies.
2) Tracking - for a symmetric bipolar output.
3) Series - for higher voltages, or asymettric output.
4) Parallel - for more current.
The data sheet PDF on the web site provides a good overview of the modes of operation, and how they can be used.
Hope this helps.
Steve.