Hello there,
I recemtly get an a-100 low cost case and reading the manual says tha accept Doepfer modules or 100% compatible, so im wondering which other providers or modules can i use with this case. Thanks in advance.

Any Eurorack except for early Analogue Systems modules, which have a slightly different power connection setup. These can be made to work with an adapter power cable, but then you face the issue of their earlier modules not lining up with the mounting spacing. More recent Analogue Systems modules now have the proper connection for the Eurorack standard, plus these use oval mounting holes to allow them to line up with both AS-Euro cabs and more typical Eurorack cabs.