If you have the old Packard Bell and it is still working, you should be able to ascertain the voltage(s) and their polarity.
Maybe its manual advises these details.
If you cannot meter at the socket itself, it may be necessary to cut a short length off the speaker power cable including its plug. Strip the cable ends, connect to the Packard Bell and meter such.
Or meter from inside the speakers themselves.
Then install a 'standard' plug on the speaker cable and connect to a *SUITABLE* power source.
Do try and ascertain wattage to be on the safe side, which should be detailed somewhere on the speakers.
Good Luck - Keep us posted.