Power Supply Tips by LOG

My cousin asked me, the Lazy Old Geek, how to buy a power supply for a laptop. Here are some quick tips.

The first two pictures are a laptop power supply and a ‘wall wort’ power supply (I have no idea what it was for).

Power supply labels typically specify:
Input: the electrical requirements coming from the AC outlet.
Voltage: often a range
          Type: usually AC, sometimes AC is indicated by a (~) wavy line.
          Current: in Amps (this is the maximum required, may draw less)
          Sometimes Hz: 50 or 60Hz, for this type of supply
Output: the requirements coming out of the power supply
Voltage: a fixed voltage
          Type: can be DC or AC sometimes indicated by a (~) wavy line.
          Current: in Amps

There are several pictures of various power supply labels.

Important Tip: The most important information is the output voltage and current (and type). The voltage is fixed. The current is maximum. What you connect has to require the same voltage (and type). The power supply will supply any current up to the maximum specified, e.g., you can hook up a 5VDC 0.5A wi-fi adapter to a 5VDC, 200A supply.
USE: I am an electronic hoarder, so I have probably 20 power supplies. This information will allow me to find a substitute power supply for a device or a new one for an Instructable project. Make sure the power supply voltage and the device voltages and types are the same. The power supply current can be the same or higher than the device. I was also able to supply my cousin the information she needed to get a replacement laptop supply.

Pictures: laptop label and router label. Devices connected to a power supply.
Input Voltage: fixed voltage
Input type: AC or DC
Input current: is the maximum current to power the device. It may use less.

TechnoTip: The last picture shows the measured voltage for a 19V power supply. Notice that it is higher (19.6Vdc). One of the reasons is that it is unloaded. There is no device connected to it. But it might be slightly higher or lower even when connected.

Less Important Tips:
TIP INPUT Voltage: I am fairly certain all countries have AC voltage outlets. This can be 100, 120, 220 or 240V. Just make sure your voltage is in the range.
TIP INPUT Current: This is the maximum the power supply will draw. Typical current will be less. This isn’t important unless the current exceeds the maximum for your AC outlet. U.S. residential outlets are rated at 15Amps.
TIP INPUT frequency: Every country I know of has either 50 or 60Hz. For power supplies, I would guess any should work any where. Where frequency is critical is for AC motors.
Tip Type: Some manufacturers label voltage as AC or DC, some will use the (~) wavy symbol for AC and the solid line over a dashed line for DC. I think thes symbols come from what the voltage looks like on an oscilloscope. AC is a sine wave. DC is a straight line above the ground level. Ground is represented by the dashed line.
Tip Connector: some labels have an additional diagram. This shows how the DC voltage is connected to the connector. The connector is in the middle. The dot shows the polarity of the center pin (positive). The C symbol is the outer connector (negative).