I am a certified electronics technician:
Voltage goes up, current goes down
current goes up, voltage goes down
When you observe a power supply it has 2 ratings, in most cases.
1) Voltage
2) Amperage
This means that the power device is designed to send exactly that! Nothing more, nothing less!
Remember that any device that requires a power supply in order to operate, does not have an internal power supply. This means their is no circuitry that comes with a power supply in such device. For example, a bridge circuit (Converts AC to DC), a regulatory circuit (The section that adjusts or fine tunes the DC output) and there is more... but enough said.
What this means is that what you apply is what it tries to use, and cannot self adjust for any changes. And if you apply the wrong thing.... well...
More over, This is why small devices need a power supply, because without it, one can't manufacture something as small as it is.
Lets make a chart:
Device Expecting _____ Power Supply Out (+VCC) _____ Actual Results
--------------------- _____ -------------------------------- _____ --------------------------
12V & 500 Milli Amps _____ 12V & 500 Milli Amps _____ 12V & 500 Milli Amps
12V $ 500 Milli Amps _____ 5V & 500 Milli Amps _____ 5V & 1.2 Amps
|
+--- This one fries the circuits and psychically burns the lines/wires with way too much current and can actually start a house fire. When the device stops working you smell the burn.
5V & .75 Amps _____ 5V & .75 Amps _____ 5V & .75 Amps
5V & .75 Amps _____ 12V & .5 Amps _____ 12V & .1 Amps
+
+--- This case is not a fire hazard and is the silent killer. The device cannot take the pressure of doubling the voltage without a regulator and physically ionizes the parts, resistors, capacitors. When the device stops working you usually smell nothing.
The clock radio you plug into the wall next to your bed? Do you think it is actually using 120V AC Power? Of course not!
The clock has its own power supply built in, and it also uses 5 or 12 volts DC. If the voltage during the day changes from 110V up to 122V and down to 108V the DC output on the power supply does not change and stays at 5V/12V DC because of the regulatory circuit.
A small external power supply does not work like the bigger internal power supplies. They do have a regulatory circuit just the TV or Radio and produce the same 5V or 12V DC not matter what happens to the AC power in. Not only does it maintain the same Voltage, but it maintains the same Amperage. So think about that next time you say, "HEY I THINK THIS IS THE POWER SUPPLY LET'S PLUG IT IN AND SEE IF IT WORKS?" BAD IDEA!
Always check the ratings on the device, and on the power supply, if they don't match, DON'T PLUG THEM IN! OR ELSE! GUARANTEED!