The output of a 12 volt transformer is an alternating current (AC). Your adapter is a 12 volt transformer but it has a built in half wave or, more expensive ones, a full wave bridge rectifier. What this rectifier does is change AC to DC. Bridge rectifiers are cheap to purchase. Connect it to the output of the 12 volt transformer and you will get a DC voltage. Great little project.
Use a voltage devider or a transformer.
No you shouldn't. Doubling the voltage will double the current through the device. This in your case will apply 24volt to the device connected to the downconverter and will burn it out.
Depending on what is connected. Check the specifications for what you're using the transformer for - is 2500mA needed, or is less than 2000mA needed? If more than 2000mA is needed, your transformer will overheat and fail eventually, so it's not a good idea. Bigger is always safer.
A 15-volt transformer can potentially replace a 12-volt transformer for an LED aquarium light, but it may not be advisable. LEDs are typically designed to operate at specific voltage levels, and using a higher voltage could lead to overheating, reduced lifespan, or even damage to the LEDs. It's best to use a transformer that matches the voltage rating specified by the LED manufacturer to ensure safe and optimal performance.
Step down transformer.
No, the 12 VDC light must have a DC supply and the transformer voltage as well as being 16 volts which is too high, the output is AC.
No you shouldn't use a 14 volt 5 amp adapter on a 12 volt 5 amp device unless you know for sure that the 12 volt device has an internal voltage regulator that will lower the voltage to the correct voltage range the device was designed to use. As long as you always take care to check the output voltage with a voltmeter first, to be sure that the voltage from the adapter is regulated, meaning that it does not rise when a lower current in amps is drawn from it, you may be able to use an adapter that gives the right voltage at a higher amp output rating than the device actually takes. (For example, it may be possible to use a 12 volt 7 amp adapter for a 12 volt 5 amp device.)
Reduce the primary voltage and the secondary will also drop.
To change the voltage of a 12-volt battery to a 6-volt output, you can use a voltage regulator or a step-down transformer. A voltage regulator will reduce the voltage to the desired 6 volts, while a step-down transformer will step down the voltage from 12 volts to 6 volts. Both options will help you achieve a stable 6-volt output.
Look at it and find its weight. If it is heavy it contains a transformer and is dimmable. If it is very light and obviously contains no transformer, it can't be dimmed.
To power ten 12 volt 10 watt lights, you would need a transformer with a total output of at least 120 volts and 100 watts.