Important considerations when choosing power supplies are type of output, regulated or unregulated. Regulated means the Voltage will stay constant (at least while the supply is operating within its specification) irrespective of the load. Unregulated supplies tend to have higher outputs than stated and are normally used with equipment that has it’s own internal regulation circuitry. If in doubt always choose a regulated supply. Using Voltages higher than recommended for a particular piece of equipment may cause permanent damage. Where Wattage or VA rating is quoted this often refers to the total wattage available for a power supply. This figure is mostly used for multi rail units, so that when the VA is calculated for each output and then added together, the total Wattage / VA should not exceed the makers rating.