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I have several laptops of various brands. Each has an AC adapter that's designed for the specific computer it came with. I also know there are universal adapters can adjust their voltages automatically to be compatible with multiple models.
I'm able to use AC adapters from different companies that have the same voltage regardless of their amperage rating (assuming they're physically compatible), yet if I use two adapters with different voltages and the same amperage, it either fails completely if it's too low or, from my experience, if it's too high something inside the laptop sizzles and pops and the computer's now a brick.
I know that you can use a power supply with a higher amperage rating than you need because electronics don't have to draw 100% of this to function. They need at least their rated amperage, but any extra won't hurt.
A lot of people shop for power supplies based on wattage. That seems to be the golden cow of computer power supplies. When looking at laptop power supplies, however, it isn't very helpful.
The only laptop adapter I have that even lists wattage says:
12V --- 4.0A
- MAX 49W -
I understand that there's a formula for determining watts from volts and amps, yet the max wattage on this power brick is very close to watts times amps. Many laptops have desktop grade parts, yet they come with these same power supplies.
Edit -
Clarification: How can a small AC Adapter give a laptop enough juice to run a desktop grade GPU when a desktop PSU is much larger and requires a fan and heatsinks?
Wattage is equal to volts * amps – wizlog – 2011-08-26T20:34:23.597
Not everyone shops for watts - stability of the load is more important to me. Wattage does matter a bit with desktop systems in that you can add a lot more hardware (multiple hard drives, dual optical drives, high powered sound cards, etc), some of which can be very power intensive (high end video cards, sometimes more than one). Since you won't be adding these types of devices to a laptop, the wattage of the adapter isn't an important consideration - it is designed to work perfectly with the hardware in the laptop. – MaQleod – 2011-08-26T20:34:25.407
Could you clarify what you're asking? I see a lot of text about your AC adapters and then something about wattage, but I fail to find the connection between the two. – digitxp – 2011-08-26T20:36:06.373
I'm asking how wattage works in relation to laptops. – Tyler Faile – 2011-08-26T20:54:49.653
It's important to note that, when it comes to power supplies, more power is not necessarily better. An oversized power supply will waste more energy, and will likely regulate the output voltages more poorly. It's best to "right size" a power supply, and pick one that's adequate but not excessively large. – Daniel R Hicks – 2011-08-26T21:11:34.940