How do we know if these are doing something else?
This is a good enough "policy control" for the average consumer.
Tread with caution...the prospects of zombie grift tend to be real when brand recognition is established.
[1] https://usb.org/sites/default/files/vendor_ids051920_0.pdf
When baseline consumer behavior is sort-by-price-low-to-high and select the cheapest item from random pop-up white label chinesium third-party vendor on Amazon, exercising an ounce of supply chain due diligence where none previously existed can go a long way.
To be sure, if you think you can economically defend against a coordinated supply chain attack by a speculative adversary willing to pony up real capital operating an otherwise legitimate facade for years building market goodwill only to burn it all down in one shot against a single worthwhile target...well, I've got a bridge to sell you.
It's nice to one-off check a new cable to know what it can be used for, with the additional benefit of seeing the power curves for the higher models (e.g. see a charger's power output drastically drop down as it overheats)
Otherwise AVHzY is I think the recommended brand, with two levels or pricing depending if you want external output.
The normal PortaPow tells the device that it's a charger.
The extra paranoid version with no components on the board will often limit charging, it depends on how the device treats a complete lack of data pins.
But if you're worried then get one that has a resistor and only a resistor.
If you want to block attacks that use the external data pins, then a USB condom will keep you safe. Regardless of whether it has a chip in it.
If you want to block standalone attacks from a malicious cable, then a USB condom wasn't going to help in the first place. For standalone attacks in particular, the risk from a chip-having condom is similar to the risk from a cable, but a cable can use bigger and scarier chips than the one in the PortaPow.
Transparent casing, no-chip design and custom made USB connector with data pins visibly removed means you can be sure the blocker is secure.