# Reading and understanding electrical specs on laptop AC adapters

My Dell laptop comes with an AC adapter with the following specs:

65 W
Input AC: 100 - 240 V, ~1.5 A, 50 - 60 Hz
Output DC: 19.5 V,  3.34 A


My HP laptop:

65 W
Input AC: 100 - 240 V, ~1.7 A, 50 - 60 Hz
Output DC: 18.5 V,  3.5 A


I have 3 questions:

1. On the Input AC, why 1.5 A vs 1.7 A? I just have one type of power outlet for everything, such as lamp, TV, refrigerator, etc. So this number is not too significant?

2. The output DC voltage and current are different. Would it be safe for me to interchange the adapters, i.e. use the HP laptop with the Dell AC adapter and vice versa. Which way would be safe and which is not?

3. If there's another adapter with the same output DC but higher wattage, would I be able to use it as well?

First, the over arching thing is that if the voltages match and the charger can supply more current the the original you were given, you are fine. If it supplies less, it may still be enough, especially if the battery is already charged.

1. Your wall socket will general be able to deliver in excess of 15A(depends on your country). The input current they expect is based on how much power their circuit actually uses.
2. Actually, their voltage is different, which is normally a larger issue for the adapters but the reason that interchanging is somewhat safe is for a hidden reason. Let me note first, plugging in a mismatched adapter can damage your device, and easily, if it is not able to handle the voltage you are going to supply. Most adapters user a communication protocol to verify the adapter was purchased from the original equipment manufacturer(OEM). If they do not detect this they often limit their power draw to "protect" the charger. This gives the advantage of protecting the charger if it is underrated.
3. Yes, you should be able to if the computer believes it is acceptable to use(no comm protocol to recognize a mismatched adapter). This voltage output is what primarily determines function. In electronics voltage controlled circuits are much easier to generate and use. This gets a bit too detailed, but I hope this information helps.
• The OP does not say where in the world they are. The output current capability for any mains power outlet will be dependant upon local specifications. In the UK the max is 240V(nominal) 13A. The European plug is rated at 16A, Australian/ZZ at 10A and the North American at 15A. What standard gives 20A? – uɐɪ Mar 10 '11 at 10:08
• @Ian, I will edit to 15, I must have mixed it up. Honestly, I thought they often wired houses to go in excess of 20 here but are required 15A. I do forget, and I have only been told, never verified. – Kortuk Mar 10 '11 at 10:45
• I think new/renovated homes in the US (or MI at least) require 20 A circuits to outlets (or it may be that they require 12 AWG, which is rated for 20 A anyways) – Nick T Mar 11 '11 at 3:20
• @NickT, thank you for letting me feel a little more sane, I have been told 20A by more than one person and over years. I tried to easily find a simple document to link to for standards, that was not a simple task. – Kortuk Mar 11 '11 at 9:04
• I do not believe that you 2nd point about communication protocols is true. I disassembled a Macbook charger once and while I did find funky stuff inside (like a CoolMOS! never seen them in practice before) there was nothing suggesting any serious logic on the output end (and the cable has only 2 wires). – jpc Mar 11 '11 at 10:53

The AC current rating on the power supply label indicates the maximum steady-state current draw at the lowest specified line and the maximum specified load. If both power supplies are delivering 65W on the nose, the one drawing 1.5A may be marginally more efficient than the one drawing 1.7A.

It's usually not a good idea to use an adapter set to a higher voltage on a piece of equipment expecting a lower voltage. The device being powered could end up dissipating higher than expected power, causing possible thermal issues and/or shortened life.

Using an adapter with the same voltage and higher current will be OK as long as the device being powered doesn't have a fault. Having more power available to crank into an abnormal condition can lead to bad things like fire. If we're talking a few extra watts, that's one thing. A few hundred more, well, that could be dangerous...

2) I wouldn't do that. Laptops repairs are quite expensive. Aftermarket chargers, not so much. ;]

In any case you could try using the one with lower output voltage with a computer expecting a higher one. But it may not work properly (like powering but not charging and such).

3) Yes.