Okay, I've encountered some devices recently (in particular some replica lightsabers) which use which refuse to charge via their USB-C ports unless it's an A-to-C cable. Tried multiple known-good C-to-C cables and it wouldn't charge, but an A-to-C cable always works fine.

So my earlier statement about cheap cables was wrong.

I wonder if it's because these things, under the hood, have cheap charging circuits which are just old 0.5a chargers but they use the USB-C plug for compactness and supply a cheap A-to-C cable so that it works.