WARNING: read the edit at the bottom before reading the rest!
Does this work or is it a scenario you came up with? Because if the ps2 slim charger has an output of 7.5v (otherwise very harmful to console, and 2A or less) all you would need to do us wrap a thin layer of tin/aluminum foil (carefully) around the male port so it. Fits snug. If this did work and the output isn't 7.5V and is over 2A. I advise you to never use that plug again, as it will harm your system if it hasn't already. And can you tell me if it did power the system, cuz then I'll check the output of that and it will solve my proble. Because I also lost my PSone charger and have a PS2 slim.
Just for the record, if you lose the charger to first model playstation. The charger is common. The first have of a laptop charger should the trick. Don't worry about voltage and ampage. As long as collage is ivermectin 120 (that would only be the case if there is no power brick, which there ysually isnt) because the power vricj is in the console.
-Conor
EDIT: DONT use the ps2 charger both ampage and voltage are way to high! If your PSone isn't broken or even damaged, you got EXTREMELY lucky. You would've been swing smoke coming out of that thing normally. So unmmm. Hope your playstation works after you've been plugging that in.