UK Genuine / Orignal FSP 19v 9.47a AC Adapter Free Shipping

Can a different AC adapter with a different voltage and amperage be used on a monitor?

First the power requirement of the monitor must be known. This information is on the product safety label usually on the rear of the device. What is needed is the voltage and current or voltage and power requirement.

The adapter you are trying to use should match these requirements. The first thing that needs to match for the adapter is the power requirement but needs to be equal to or greater than the monitor requires. Second thing is the voltage rating of the adapter. It needs to be, I would say, within 1 volt of the requirement or maybe no more than 2v higher than the requirement. Third, the adapter current should be equal to or greater than the monitor requirement. The monitor will draw a fixed current. So a adapter that can supply more is ok. It will only supply what the monitor needs which is less than it can supply. It's like your mom giving you 10 lbs of potatoes to eat, but you only need 1 lb to eat. The rest are available but not needed. Same thing with the adapter. But the adapter needs to be able to supply what the monitor needs. So,

1. The adapter needs to be able to supply the Watts needed by the monitor.

(V-adapter) x (I-adapter) => (V-monitor) x (I-monitor)

2. The adapter output voltage needs to closely match the monitor requirement. (V-monitor -1v) <V-adapter < (V monitor + 2v)

Example: monitor rating 12vdc at 1.2a = 14.4w

Adapter rating: 13.5vdc at 5a = 67.5watts. Can this adapter be used?

That adapter has enough power to supply monitor. 67.5w > 14.4w
Adapter has 13.5vdc output. Monitor requires 12vdc. 13.5vdc > 12vdc OK. 13.5vdc < 12vdc + 2vdc = 14vdc OK.

So you could try this adapter and be reasonably sure it will work without damaging the monitor.

The reason I say reasonably sure without damaging the monitor is that the internal regulators that operate off the 12vdc, normally will now get hotter because of the higher input voltage. This could eventually cause a failure of the internal regulator if it gets much hotter than the design can handle. But this should be OK if the monitor is not used in a room that is excessively hot like 40–60°C.

My laptop is rated "19.5V - 3.34A / 4.62A", should I buy a 65W or a 90W AC adapter?

Wattage is Volts x Amps, but there’s more to it than this.

Excessive voltage can damage your device, but excessive amperage won’t (the device will only draw as many amps as it needs)

Therefore, you need to ensure that the charger you get is 19.5V. The issue then is, does your specific laptop use the 3.34amps or the 4.62? If you aren’t sure and cost is the same, just go for the higher amperage (therefore wattage) one. As long as the volts are correct, you wont damage the device.

How do AC adapters work, and why are they so large?

There are physical limits to the size, mainly determined by the size of the filter capacitors in the front-end power supply. The capacitors have to have enough microfarads to supply current between AC cycles. There also has to be a transformer and those can be made smaller, to a point, but there are limits there too.

The electronics have been shrunken down to a small flat-pack IC the size of a wood-tick, so that part can't shrink much more.

In general the supplies have gotten much smaller and lighter over the years. There is still some shrinkage possible by using higher frequency transformers but they probably won't get much less than half as small as now.