How do I know when to use an adapter or a transformer? (Israel)

General rule: read the sticker on the item you want to use, although in some cases it is a text area molded into the plastic of the transformer of the charger.

Most laptops, phones, camera chargers and such these days are made to run off 100 as well as 240 volt, and can handle 50 as well as 60 hertz.

If something is made to run on 240 volt, it will certainly run on 220 volt, and you should not use a converter.

If your item can run on 100 as well as on 220 / 240 volt, you should not use a converter, the item will not perform as well and it might even be damaged. See this link.

Hairdryers and curling/straight irons often need a converter; some are made to be dual voltage and some have a switch to chose voltage. But be careful, it is easy to overload a converter, as things that generate heat take a lot of power. Mostly it is cheaper to buy a new item, but I would say just do without.

In some cases the number of cycles per second (hertz) will make a difference. Clocks are well known for that, but electric shavers can have difficulties as well. A battery alarm clock and shaving the 'old' way will take care of that.

Some shavers may work with just an adapter. A clock may need a frequency converter, which is a far more expensive and bulky piece of equipment than the voltage converter you show here.

Look at the existing power supply (i.e. the inline brick or "wall wart" plug used to plug into a US outlet). It will say the range of voltage it allows for input. If it says "100-240 V 50-60 Hz" you can simply use a plug adapter; if it says something like "100-125 V" you need a transformer.

Most devices aren't sensitive to the frequency, but some kinds of devices are - clocks and motorized devices are definitely candidates for this - a cheap clock designed for 60 Hz will run slow on 50 Hz even if you use a transformer.

For some devices (e.g. computers) you can even simply use a matching IEC cord that will plug directly into the wall with no adapter. Older computer power supplies may have a switch that changes it to accept 240 V instead of 120. For phones that use USB for their charging standard, you should be able to simply buy a USB power supply designed for your destination country's outlets. In some cases (e.g. Apple laptops, some Samsung tablets) the manufacturer sells a kit to replace the modular plug on the power supply with one designed for a different country.

As for the reason some devices are different - there are three kinds of device, essentially. Devices that run directly on AC (such as a cheap alarm clock), need clean power and may or may not depend on the frequency of the input. Devices that use a transformer to convert AC to a lower voltage for DC have a specific voltage range they expect. Devices that use a switching power supply, however, are able to accept a wide range of inputs and turn it into a reasonably clean DC power for the device to use. Switching power supplies are often used for more recent devices both for this reason and because they are smaller than transformers.

Several quick rules of thumb:

1. Almost everything has a sticker or imprint that lists the input voltage. Look at that.

2. For the more electronics savvy: if you're just trying to do a quick inventory in your head you can usually just go on whether the device already requires voltage conversion. Computers, phones, and other things with charging batteries almost always require a switching power supply to convert the voltage to something much lower than grid power. It's usually not too hard for the manufacture to make these work with multiple voltages.

Its very simple really:

1. An adapter is when the cable you are carrying doesn't fit in the wall socket. These adapters do not do any current stepping or conversion. They are cheap and portable.

2. A converter is an appliance that takes a specific voltage and coverts it for a different purpose. These are typically rated and are almost always heavy and bulky to carry around. You only need these if your electronic item supports a specific voltage.

These days though, modern electronic devices support multiple voltages; so the need for a converter is very rare. You would need an adapter because devices are sold with adapters for the particular region.

For example, laptops and cell phones sold in the US come with a US two prong plug, which will not work in the UK where you need a three pronged plug. For this, you'd buy an adapter. You would not need a converter since laptops and mobile phone power supplies are compatible with both 110 and 220.

It does no harm to check your device, but I am struggling to find a device that I bought in the last 3 years that was rated for a specific voltage.

If you are going to use a non-universal (Universal being 110-240 V and 50-60 Hz), your safest option is to use a step-up or step-down transformer. The small adapters as you showed are good for low amp power adapters, for example cell phones.

As long as you don't want to use a hair dryer, then a small transformer is great. However all laptop chargers are universal.