Kiniki, welcome to the forum :-) You will find all the advice you need here :idea:
I must point out though, an A1200 with an accelerator and hard drive will not work reliably for long if it has the original power supply. If you look at the brick you have, can you see the power rating in Watts on it ? You may be able to use an A500 psu as it is slightly higher rated.
Enjoy your Amiga :-D
