How Safe is it to use power outlets on public transportation in Germany?

The ICE trains I rode last month in Germany had 220V outlets. Whether those were in addition to USB outlets, I don't remember noticing.

The warnings I saw regarding charging with USB outlets were for places like airports and some hotels. Hadn't heard anything about trains. On our last trip the trains didn't have have usb outlets, only regular electrical outlets.

You will find power outlets with 220V only on trains and in most buses.

At Frankfurt airport you will also find USB outlets.

On German trains it would be very unlikely to have such issues from what I think to know about Deutsche Bahn and IT security. No experience / opinion on buses (IC bus, Flixbus etc.).

Is this a realistic/plausible threat?

Yes, it is. Exactly how much of a threat to you? No way for anyone to really know.

From a technical standpoint, any place that one plugs any device in via USB absolutely could be compromised. So there is always a risk. But in order for someone to access your data would require them to install malware in whatever that USB port was connected to. In some places, that seems highly unlikely (eg on a flight - commercial airliners are generally quite secure, even when not in operation); in other places (say, some cafe or other semi-public space in China or Russia), it would be a lot simpler to install something bad in a place like that.

Also worth considering the risk/benefit ratio for someone doing this. I'd worry more about a power port in a North Korean airport lounge or one in a bar on embassy row in Moscow...the kind of places where bad actors would see it as a target-rich environment. But in the train station in Naples? I would guess that would be too much trouble to bother with. I mean, the reach of bad guys is worldwide, but there are limits to how much effort even they are going to put in to something like this. There are better/easier ways for them to pick targets.

FWIW I have a close friend who regularly goes to China for business (he works for a major US tech company), to visit his company's Chinese partner. The degree of scrutiny and security they go through every time they enter the Chinese plant is stunning; they are required to bring special work laptops that must go through extensive security checks by their IT folks before departing and upon returning. Plugging in to networks are highly scrutinized. Doing things like plugging in to some random power port in an airport are strictly forbidden. (They are also physically searched every time they walk in and out.)

Going forward, this will become more of an issue. We're still in the early days of this vulnerability. I'd expect that in the coming years, operating systems will be hardened to mitigate this threat. But it is a real threat.

When charging from any public USB outlet (airports, some aircraft, conference tables, hotel clock radios, etc.), I use the USB-Bug from Triplett. It's a great little device. For convenience, it has a second outlet from which I can charge a non-security-sensitive accessory such as a USB battery.

It's interesting to use because it shows the current draw, indicating which of my devices support fast charging and whether a given USB outlet can supply more than the specified 500 mA or 900 mA (USB 2 or 3, respectively).

Physically, this is a USB-A device. I have yet to find something that cuts the data lines for USB-C. Then again, I have yet to find public USB-C outlets.

I wouldn't worry about the outlets on trains, they are probably safe. But then again, a data blocker ("USB condom") is a pretty cheap insurance.

I stick to regular power outlets and skip the USB outlets that can be accessed by the general public; hotel rooms, cafes, airports, etc. For me, there’s no reason to take unnecessary chances. I’m not tied to my phone or tablet and if the battery runs out, oh well.

Most of these replies re: USB ports have been very useful...thank you.

I have never heard of a "data blocker", i.e. "USB condom"...I will look into that...for this forum, could you elaborate? I am not sure my German is good enough to describe this kind of device to someone at Media Markt who doesn't speak English (most do).

I purchased a portable battery for about 6 euros at a Real store when I first arrived on this trip, and it works great for about 2.5 full charges of my phone when I am out and about in 40 degree (F) weather (YMMV). This seems to be a great option while wandering about town and/or one doesn't trust publicly available USB ports.

While I had USB ports available at my seat on my train (ICE-2nd class) from Frankfurt to Berlin a couple of weeks ago, I did not have any USB ports or power outlets on my most recent train trip (ICE-2nd class) from Berlin to München....go figure.

In German it's a USB-Datenblocker or USB-Kondom.

Are there also standard power points to which you could plug your usual charging plug (with appopriate adapter) and charge as you usually would at home? This would negate any potential, and in my opinion, extremely low threat of exposure to malware.

I have never heard of a "data blocker", i.e. "USB condom"...I will
look into that...for this forum, could you elaborate?

A USB-plug has four pins, two for power and two for data. A datablocker only connects the power pins, so there is no way to transfer data.