You could search eBay or Google Shopping for 2 of the power adapters,
both with 9V DC output and anything exceeding the KVM's 250 mA draw. If
the KVM's power jack is 5.5mm for barrel size, buy one power adapter
with the 5.5 mm outside diameter and 2.1 mm inside diameter, and another
with 5.5 mm outside and 2.5 mm inside. For $5 apiece, that's $10 and
one would have the right sized inside diameter for the pin in the male
jack in the KVM.

9V DC power adapter, 5.5mm outside, 2.1mm inside
eBay search: https://www.ebay.com/sch/i.html?_nkw...+power+adapter
Example: https://www.ebay.com/itm/9V-1A-DC-Ch...eada:rk:1:pf:0

9V DC power adapter, 5.5mm outside, 2.5mm inside
eBay search: https://www.ebay.com/sch/i.html?_nkw...+power+adapter
Example: https://www.ebay.com/itm/9V-1000mA-1...V 3:rk:3:pf:0

You probably already have something with the barrel plug that you could
test in the KVM's power jack. If you have anything with the coaxial
plug that fits into the KVM's power jack, that would tell you the
outside diameter for the plug. Then use the wikipedia article to tell
you what is the inside diameter(2) for that outside diameter of the
plug. You might find you have 5VDC power adapters you can test (but
unpowered) just to see which ones fit into the KVM's power jack. Once
you find one with a plug having the correct plug outer diameter (barrel)
and inner diameter (pin), you'll know what to look for in a 9V adapter.

I wouldn't bother with a power adapter that requires adapters at the end
of its cord to mate with the KVM's power jack: just another point where
an accidental disconnection could occur along with more connectors that
could have oxidation or debris on them. If all you know is the outer
diameter (barrel size), you could buy a 9V DC power adapter. If that
works, you're done. If the pin size (inside diameter) is too big or too
small, buy another 9V DC power adapter with the other pin size.