Hello!
There's a brief line in the CRS109-8G-1S-2HnD-IN specs that it's 802.3af/at compliant.
However, I'm trying to power it up from D-Link DGS-1100-08P that supports 802.3af PoE out, but no luck.
I've tried a straight cable and a cross-over one (1 - 3, 2 - 6, 3 - 1, 6 - 2, other wires as usual).
Should I tweak something to make it work?

Hello,
PoE in: Passive PoE
https://mikrotik.com/product/CRS109-8G-1S-2HnD-IN

In brochure there was written "802.3af/at compliant", that is a mistake, it simply support up to 57V on poe-in.
Sorry for any inconvenience caused .

Thank you for the quick answer!

The specs provided by your link still feature 802.3af:

Powering
Details
802.3af support yes

Also there was a mention of 802.3af/at in the short product description, not only in the brochure, now it's gone.

Looks like you guys had wrong specs for this switch for years and nobody noticed it.
It's really sad, because I was relying on this feature buying this product.
Now I have to rethink my setup and waste more money

Does the D-Link support passive POE out? If it does, then it should be able to power the switch.

Looks like it doesn't. There's some ambiguous option "Legacy Support" that can be enabled, but enabling it makes no difference.
AFAIK, Passive PoE mainly used by Mikrotik and Ubiquiti, so I doubt it's widely supported by other vendors.