Shahzad,

Power Supplies have two major categories.

1) Linear
2) Switch mode

Linear power supplies use linear voltage regulators and are excellent regarding volatge regulation and have very low ripple in the output. However, these can only work if input voltage is more than output. Power raing is upto few watts since these dissipate too much heat if large output currents are required. Generally, as a rule of thumb

Heat produced= (Vin - Vout) x I

Switch mode power supplies regulate the o/p voltage by chopping the input power, at certain frequencies and pulse widths. They can be used as step-down and step-up as well. Further, there are lot of topoligies in SMPS, like flyback, forward mode etc. Power dissipation is minimum, and voltage regulation is not as good as that of a linear type. However, high output currents/power is possible in small size as compared to linear type. These have high efficiency as compared to linear type. But these can produce EMI/RFI which has to be taken care of.

I wil recommend "SWITCH MODE POWER SUPPLIES" by Marty Brown,

For you application, (+5, -5, +12 and -12) you did not mention the currents. If it suits you, you may use an old PC's power supply (AT style ). If you use ATX type, you will have to connect GREEN (Shut Down) wire to ground.


Regards

IA