No, 12 volt AC is a different from 12 volt DC. Have a second look at the 12 AC volt adapter's output label. Most adapters contain a bridge rectifier in them that makes a conversion within the adapter. An example of this is in phone chargers.
To increase a 4.5 VAC supply to 5.5 VAC, use a transformer. To increase a 4.5 VDC supply to 5.5 VDC, you'd need a boost converter.
24 VDC or may be 110 VAC
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Yes, there will be no problem with this adapter. The 1 amp device will only be drawing half of what the adapter can produce.
It depend on what the load of the device that plugs into it is. The mA rating is the maximum amount of amperage that the adapter can produce. The 500 mA adapter will produce about a half amp whereas the 1200 mA adapter outputs 1.2 amps. So one is about three times larger that the other. Check the device that you are trying to power for a mA load and that will tell you whether you can use it on the 500 mA adapter.
Voltage is a general term. VAC & VDC are specific terms.
It will burn out violently, possibly exploding, sending broken glass everywhere.
No, if the device requires 12 VDC then no substitute adapter of a different voltage will work.
Yes, between 40-50 vdc but up to 120 vac when it's ringing
Yes, the adaptors mA name plate capacity is the maximum amperage that can be drawn from the device. The load of what is plugged into the adaptor is what governs the draw from the adaptor.If the adaptor with the 350 mA maximum load worked, then the 450 ma adaptor has more than enough capacity for the connected device.Just make sure that the adaptor is the same output voltage type. Some are rated at 12 VAC at 450 mA, while others are 12 VDC at 450 mA. The output voltages must match to be interchangeable.
The coil will burn out due to having almost double the voltage being applied to it.
The transformer for n HO scale train has a primary voltage of 115 volts. There is a tap off for accessories that is 17 volts AC and a rectified DC voltage to apply to the track at 10 VDC at 1 amp.