Which ADSL modem works well with an Apple Time Capsule?

Question

ADSL

Bought a Time Capsule but couldn't get it to work properly with my old D-Link DSL-G604T.
Separately, everything works fine, but together it's bad.
If the Time Capsule acts as a router, then the backup speed is excellent, but Internet access is very slow.
If the router is D-Link, then a very slow backup but a good access speed.
I tried a simple Acorp Sprinter @ ADSL + ROUTER LAN110, everything was set up by itself and flew smartly for exactly 2 weeks.
Then everything mysteriously went wrong, and without my intervention, it was no longer possible to achieve success.
I would be grateful if you share your practical experience and advice.