I have a Sony Vaio PCG 61212W laptop.
Because I got it from India, I needed a Uk power cord. I therefore ordered a power cord which is 3A and 250 volts. But the one I have with me currently reads 2.5A and 250 Volts. Would this cause any harm to my laptop?
No, this won't cause any harm. The UK power cord is simply rated for higher amperage, meaning it can have more current flowing through it than the Indian power cord. The adapter itself will almost certainly have a lower amperage anyway, and in any case the laptop will only draw as much current as it requires.
Note: this assumes that you only bought the power cord (the part that goes between the adapter and the mains outlet). If you also bought a new adapter (the brick with a second cable leading to the laptop), then see the other answers below.
If you are talking purely the "power cord" -- a piece of wire with a connector on each end and no "box" of electronics somewhere along its length -- then it really doesn't matter. My Vaio draws 1.3 amps, according to the power adapter, and any cord with an amperage rating higher than that and a voltage rating higher than the local line voltage is fine. (And it would be rare to find a power cord that was below 250V and 2.5A.)
If you're talking the power adapter -- the box of electronics in-between two pieces of wire -- it's OUTPUT voltage should be within about 0.5V of your computer input, and it's OUTPUT current should be larger than your computer's current drain. (Plus of course, the output needs to be DC, and the negative and positive terminals need to be correctly oriented at the plug going into the computer -- a diagram on the adapter will generally show the +/- orientation of this plug.)
And, as a general rule, so long as a power supply has essentially the same voltage (within about 5%) and a current capability greater than what the device demands (and proper connector polarity) then it should be fine. The only exception would be that it's unwise to use a power supply with a MUCH HIGHER (ie, 10x) current rating than what the device requires.
Here's the deal. The voltage SHOULD match (power adapters provide a steady voltage over a range of currents), whereas the current MUST meet or exceed.
You should be able to use this adapter.
When selecting power supplies: Match the voltage exactly. You can use a power supply with a higher rating on current (amps) or total power (current * voltage, so directly related anyway).
Do not use a power supply with a lower current rating or power rating than the original.
Hope this helps... :)
Can I use a charger with less Ampere than the original? Maybe. But from what you're saying, the new charger has MORE Ampere than original.
So your 3A supply should work. You need to simply match the voltage at the output stage and provided the current rating is equal to or greater than what you have, it should work fine.
Others haven't mentioned this but you also need to make sure the connector polarity matches. Some are positive centre tip, some are negative centre tip. The after market power supplies will usually come with a range of adapter tips so make sure you choose the correct one. If the laptop is well designed even getting it around the wrong way will not cause any damage.
If the current rating is less than the original 2.5A then what you could do is put extra strain on the power supply to the point where it may overheat or fail to work at all.
In every case the laptop will only draw what it needs (or try to). Current draw on the power supply will actually vary depending on what the laptop is doing. e.g. charging vs, not charging and whether you're doing work that requires a lot of power like playing graphics intensive games etc.
Normally, the amperage rating for the power supply is chosen to be slightly higher than the maximum draw from the laptop. Which means you could even get away with a slightly lower amperage supply, but I wouldn't choose one less... it's asking for trouble.
