Thank you all for your inputs and interest in the topic!
I'd been wracking my brain trying to research dianzi and dalachi. It's especially tricky given I have to rely on translators.
What I've found is that dianzi (钿子) translates literally to 'hair pin'. Which means it likely just refers to the hair ornaments, so the term itself has been used wrongly by me. I believe the correct terminology for Junko and Skadi's headwear would be the Qitou (旗头), which is the umbrella term that covers dalachi, liangbatou and any other headwear that resembles overarching hairbands. It translates literally to 'flag head'.
Here is some image examples of different variants; and some more here, here, here, and here...
Here is a gif of an actress trying on a qitou, to give a better view.
Basically, Qitou come in a variety of sizes and shapes, but they share the characteristic of resembling headwear (or hairstyle) that arches over the scalp, similar to a tiara or - like its literal translation - a 'flag'.
@shemingwan_wen I agree, the phoenix crown wiki is vague. The tag is full of mistagged headwear. :HinaUoh:
@Iroshi Please let me know what you think about this revised input (sorry about the response delay).
@Marble_Crescent If you image search 鳳冠 (Chinese for Phoenix Crown) on a search engine, the visual results are very different from Junko's headwear. Or even just the Wikipedia page.