What conversion can and cannot restore
Converting WebP to PNG produces a lossless file, but lossless here means "no further loss from this point", not "original quality restored". If the WebP was encoded in lossy mode, the detail its encoder discarded is gone permanently. The PNG faithfully preserves the compressed result, artefacts included.
There is a common misconception that converting to a lossless format repairs an image. It cannot. What it does is stop the degradation: once in PNG, the file can be opened, edited and re-saved repeatedly with no further loss, which is exactly what you want if the image is about to go through several editing rounds.
Expect the PNG to be considerably larger — often several times the WebP — since it is storing every pixel explicitly, including the artefacts. That is the normal trade, not a fault of the conversion.
Transparency and animation
WebP supports an alpha channel in both its lossy and lossless modes, and PNG supports full 8-bit alpha, so transparency converts cleanly with no compositing decision required. This is the one area where the two formats map onto each other exactly.
Animated WebP is the complication. It holds multiple frames like a GIF, and PNG holds exactly one. Converting an animated WebP therefore forces a choice: extract a single frame, or move to a different format. APNG preserves animation with far better colour than GIF but has narrower tool support, while GIF is universally supported and limited to 256 colours per frame.
If the goal is a shareable animation rather than a still, converting to GIF via the GIF tool is usually more practical than APNG, purely because everything accepts GIF.
When you actually need PNG
The usual reasons are compatibility rather than quality. Some older design software, print workflows, email clients, and a surprising number of content management systems and marketplace upload forms still reject WebP. PNG is accepted essentially everywhere, which makes it the safe interchange format.
It is also the right target when an image is going into an editing pipeline. Repeated saves in a lossy format compound artefacts, so converting to PNG before a round of edits and exporting to a delivery format at the end is the correct order of operations.
For final delivery on the web, though, converting WebP to PNG is usually a step backwards — you are trading a smaller file for a larger one with no visual gain. Keep the WebP for the site and use the PNG for the tool that will not accept it.