Convert DSC power adapter to DC

So quick rundown here. I had a DSC alarm system, power with aN AC power adapter that runs with 2 18 gauge copper wire plugged in in the attic. My question is, since I already have this 18 gauge copper wire ram to the alarm panel area, can I change the power adapter to DC so I can power 2 connected devices, 1 siren, and 1 tablet. I hate to have to keep the old alarm panel up just as a pass thru. Any ideas on whati can do?