|Hi Voice, you advise the Sony (what model?) is old.|
Because of this, I wondered if the 7.7 amp psu is original, and if NOT, could it be a higher amperage than the original psu.
On the laptop, may be a label providing details of the required psu rating.
It is never a problem if a replacement psu has the same voltage and the same or higher amps than the original. (same with the battery). Although for the battery, it is my opinion it is unwise to have more or less cells than the original (generally 6).
There could be a (serious) problem should an incorrect voltage be supplied and/or lower amps than the original.
Possibly a modern light weight psu can be found with the correct rating for your laptop.
Good Luck - Keep us posted,
message edited by Mike Newcomb