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Dennis:
I don't know what is being implied in your case.
A constant voltage supply, whether DC or AC, is ideally a source where the output voltage is constant independent of load. This means zero equivalent internal impedance. Never really achieved, but with electronic circuit control can be very good. It may be possible to build a 10 V DC 10 A supply where the voltage changes less than 0.001 V from zero load to 10 A load. This is a voltage drop of 0.01%.
For a residence a 5% change might be considered constant voltage.
A Sola constant voltage transformer I have is rated 95 to 130 V about 100 VA (1960 nominal voltage was somewhat lower than today) has the following results:
Load change --- With 115 V input the output changes from 123.3 V at 0 load to 120.5 V with 100 W load. These are not designed for load regulation.
Constant 100 W load and regulation relative to input voltage ---
095 121.1
105 120.9 diff 0.2
110 120.8 diff 0.1
115 120.5 diff 0.3
120 120.2 diff 0.3
125 119.8 diff 0.4
130 119.4 diff 0.4
135 118.8 diff 0.6
In the mid area the regulation is about 0.25 % per 5 V change. Over the range 95 to 130 it is about (1.7/120)*100 = 1.4 % per 35 V change.
A constant current source is one where the current is constant independent of load. Quite obviously there is a physical limit here. We can not go to a large resistance load without the voltage becoming excessive. For example 1 A into a load of 1 megohm. But, within reason, we can do pretty good with electronic control.
Consider an LED diode itself. The voltage drop across the diode in the forward direction may be in the range of one to several volts, and for a given current will vary with temperature. Brightness is a function of current. Suppose we applied a constant voltage to this device, then its brightness would be a function of temperature, and interchanging different LEDs, because of manufacturing differences, might cause differences in brightness. Thus, the LED chips themselves must be supplied by a moderately constant current source. If you have a 12 V source and one LED, then a series dropping resistor is usually sufficient to provide an approximately constant current. But, in high power applications this is power wasting. Electronic circuitry is used to solve this problem.
I have DC power supplies that are both constant voltage and constant current sources, but not simultaneously. Generally these are constant voltage supplies with current limiting above some current level. Some are fold back on the current limiting.
The manual on your power supply may tell us what they mean by constant voltage/constant current, or experiments on the supply may be needed.
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