I’m planning to go to Germany in a few weeks and need to get a power converter. Some are a simple plug device and others have a transformer (?) with plugs. What’s the difference and what do I need to buy?
Look at the devices you want to use. Most appliances and power bricks can handle the different voltage (230V) and frequency (50Hz), in which case you only need a simple plug. If for some reason your device can’t handle the difference, you’ll need a transformer.
The simple plugs do not convert voltage (so you will get the higher European voltage), the bigger “transformer” ones do.
As ** Pitchmeister** notes, most consumer electronics chargers made in the last decade tolerate the higher voltage just fine, so if that’s what you have, you just need the plug converter to physically fit in the outlet. If you have a more “primitive” appliance (like a hair dryer or something) there’s a good chance you’ll need the transformer.
Depending on where you are staying you might not even need a plug converter. Many major hotels have receptacles that take US plugs as well as Euro style. But a few plug converters are always good to carry, and there’s not much to them so any one will work just the same. If you plan to travel to a number of places that use different plugs types a single universal converter is handy, but if you’re just going to Germany then it’s overkill.
Aside from hairdryers and household appliances, not much these days requires a transformer.
To clarify the (good) responses so far: any device made in the past 20 years or so has an indication, on the device itself or on its brick, of its voltage and frequency requirements. You may need a magnifying glass to find them. The voltage in Germany is 230 volts and the frequency in 50 Hz. If your device can tolerate that, you only need a plug adapter. If it can’t, you may be able to use a voltage transformer, which will give you 120 volts but still 50 Hz. If your hairdryer isn’t compatible, keep in mind that many hotels supply one. For devices that connect via USB, you could buy a USB brick in Germany for a few euros.
My only “add” to the great comments is to really think about whether you need a transformer. In my experience they are really heavy and can be expensive - especially for one powerful enough to handle a hairdryer etc.
If you need it for something like that, (assuming your hotel doesn’t provide), I’d recommend buying a cheap hair dryer in Europe and giving it away when you leave.
A friend’s teen daughter was travelling in Asia and I warned her that her hair dryer wouldn’t work with a simple plug adapter. Like many teenagers she only learns from personal experience (i.e.: you can’t tell her anything). She brought her expensive blow dryer and straightening iron from Canada and burned both of them out the first day. At least that lightened her luggage 
One important detail when traveling with a laptop from the US to Europe, or when using any other transformer that’s not part of the machine itself:
Plug the brick into the wall first. The brick itself has a transformer inside; doing it this way gives it the tiny time it needs to adapt to the higher current.
If it’s not a computer brick but a different kind of transformer, it may have a button you need to set to the input voltage.
We found out after a coworker fried her laptop that way. Cellphones don’t suffer from the same problem, having much more sophisticated currency adapters. Why don’t most laptops? Because they’re also more expensive, because most people don’t see a problem with carrying around a brick which weighs more than the computer itself (and may even expect it), and in fact the last desktop computer I bought came with a brick as a trick to make the box itself lighter and smaller (I don’t mind, it means my mother can move it safely).
The makings of an urban legend.
Note that for resistive loads like hair dryers or curling irons, you can get a small “chopper” power converter good for 1875W. No need for transformers.
It’s been like this for a while. Back in 2003, my mom and I went on a trip to Ireland, and we brought her camcorder (you remember those, right, from before everyone on the planet had a video recording device in their pocket). Before she left, she prudently got a transformer converter from an electronics store, that the salesman solemnly assured her would work. It wasn’t until we were there that we noticed that the converter said not to use it with any sort of battery charger, because it could damage them. So we looked in the local stores in Cork (the only urban area we stopped in), and all we could find there were the straight-through prong-shape adapters. And it wasn’t until we were out of Cork and into areas too rural to have any sort of electronics store that I took a good look at the power label on the camcorder and saw that it could, in fact, handle 230V 50 Hz.
When I traveled throughout Europe in 2001 I took a handful of plug converters and also a transformer for my electric razor, which I later found out could use the higher voltage after all. That was a bit of a bummer because the transformer was pricey and heavy to be lugging around. Though now that I think about it, I must have used the transformer for my clock radio too (I was taking classes in Copenhagen for two months). I quickly realized that was a no-go, because the clock needed 60Hz power to maintain its timing. As Heracles mentioned, the transformer converted from 230V 50Hz to 120V 50Hz so the clock would lose 10 minutes each hour, making it useless.
Forgive my ignorance, but are you saying that my cell phone and tablet can handle the voltage and all I need is a European USB brick? I found the ratings on the laptop brick (with an electron microscope, no less) and I don’t need a transformer. Yay!
Yes for the USB devices you just need an EU brick, and the laptop probably only needs a different cable or plug.
E.G. for an Apple charger.
Switchmode power supplies typically enable this and manufactures like to simplify their supply chain. Typically only the detachable cable is changed out for different regions or countries on a product.
Products like hair driers etc…are different as they often just use simple transformers and the fact that they tend to user AC internally. Products that use DC internally including every battery powered device will almost universally use universal power supplies.
As others have noted, just get out your magnifying glass and check the label on the power supply.
I had this with me on my last two European trips. It handled two cellphones and a Chromebook without issue. It has different plugs for different countries. I use it in the States too.
My wife had a hair dryer in the 1980s or 1990s with a switch for voltage input. On US voltage it was a 2-speed hairdryer but the voltage switch had an interlock with the power switch so that if you selected 220 volts the power switch would only move to one of the speed settings.
USB is, as the name implies, universal. An American USB brick will take in 120 V, 60 Hz and put out 5 V DC. A European USB brick will take in 240 V, 50 Hz, and put out 5 V DC. A Botswanan USB brick will take in whatever the heck voltage and frequency Botswana uses, and put out 5 V DC. If a USB cable can plug into it, then it had darned well better be putting out 5 V DC, and any USB device can plug into it. Your phone itself is irrelevant, because by the time it gets to the phone, it’s all the same.
USB-powered devices, like smartphones, are common enough that many hotels and other public places may have USB outlets in place, so you don’t even need a USB brick. Now, it’s possible but unlikely, that the USB outlet isn’t simply providing power but trying to read the contents of your phone, or even write malware to it. So you might prefer to plug your own USB brick into an electrical outlet.
Thank you all. I recently started using a nebulizer and guess what needs a transformer… That’s another 5 lbs I didn’t want to pack. Pffft.
Actually most USB bricks are perfectly happy to be fed with either 120V or 240V. Just grabbed one that was handy and it reads:
Input: 100-240V AC 0.5A 50-60Hz
Output: DC 5V 2.1A
It can be plugged into most any electrical grid in the world with a simple plug adapter, and this is pretty much the standard design for these things.
That works; one can also buy or make a “USB condom” for this purpose.
Re. nebulizer, what do the electrical specs on the back say?
Hey, finally a topic that I can contribute to via this long and sometimes grammatically problematic blog article. In particular, beware of the differences between actual transformers and lightweight power converters.