Hello David

> I got my modular around 10 years ago...so I don't know if it's the
> older the new. Is there any code on the casing that would tell me

have a look in the case.

An old supply has a black or blue rectangular transformer.
http://www.doepfer.de/a100_man/a100nt.gif

the new ones have a round silver transformer:
http://www.doepfer.de/a100_man/A100_PSU2.gif

> If it is the old style, would an 800mA fuse hurt

If there is a failure, which should blow the fuse, then fuse will blow
later, means at higher currents which might damage the transformer.

Florian