I just got my seagate 1tb expansion hard drive out of the shop but I can't find the original power supply, i have a very similar one but it is 4.0A instead of 2.0A
everything else is the same; 100-240Vac, 1.2A Max. 50-60 Hz 90VA-150VA and 12Vdc
will it still be compatible?
More about :external hard drive power supply compatibility
If "Amps" is the only the value that's different, and it's higher than the original power brick, it will do no harm.
Just ensure that the centre-pin polarity is the same as the original (it's usually centre-pin positive for IT equipment).