Passive USB-to-PS/2 adapters: does more than one type exist?

[Donut]

Some USB keyboards and mice have dual-protocol controllers, allowing them to be connected to a PS/2 port with a simple passive adapter. Sometimes the keyboard would have come with an adapter when new.

But, is there one de-facto standard pinout for these passive adapters? Or are different converters needed for different makes/models of keyboard and mouse? I've seen turquoise adapters with a mouse symbol on, and purple adapters with a keyboard symbol on. Are they actually identical internally?

I have some USB keyboards and want to check whether they're dual USB- & PS/2-compatible. But I only have a turquoise mouse-symbol adapter here, which doesn't work for them. It is worth buying a purple passive adapter to test?

[fohat.digs]

I have had good luck with the cheap-o passive ones, but you do need the keyboard type.

As I recall, a mouse has 3 connections and a keyboard has 4.

Just because there are pins visible in the plug does not mean that they are actually connected to anything.