Very concerning. Every single USB port charger I have was manufactured in China.
(BTW, "educational institutes" located in China still regularly attempt to hack into my computers via the internet, so as far as I'm concerned, such threats are viable.)
I would extend this to the control systems/chips in the battery-based "Powerbanks" aka "Power Packs" aka "Backup Battery Chargers", etc
(those portable battery packs you can carry around with you to recharge phones, tablets, etc when AC power isn't available). Same thing for Mobile/car chargers and power adapters
And of course, devices infected via a charger may then go on to infect other devices to which they are later connected (e.g. your computers), either via hardwire or WiFi. Depends on how sophisticated they make the malware and the effectiveness of any anti-malware installed on those devices.
This malware vector (from AC and DC chargers and adapters
caught me completely by surprise even though in hindsight it's an entirely obvious vector. Simply for convenience, I'd been using whatever charger was handy on multiple devices for some time. (For example, a tablet charger usuallly works just as well to charge a phone.)
Where possible, I will be only using chargers or charger-to-device cables in which the data lines don't exist, charger-to-device cables in which the data lines don't exist, or modifying the non-detachable USB cables such that the data lines in the cable are cut. Note: it's possible that some chargers/adapters may be designed to quit working if the data lines aren't available. Before you make any permanent modifications, that could be tested by using an suitable USB extension cable between the charger and your device...that the extension either has no data lines or in which you've cut the data lines.
...researchers from Georgia Institute of Technology have produced fake chargers they've named Mactans that do more than just charge your phone: they install custom, malicious applications onto iPhones.
Their bogus chargers—which do, incidentally, charge the phone—contain small computers instead of mere transformers. The iPhone treats these computers just as it does any other computer, but instead of just charging, it responds to USB commands. It turns out that the iPhone is very trusting of USB-attached computers; as long as the iPhone is unlocked (if only for a split second) while attached to a USB host, then the host has considerable control over the iPhone.