need help fellow tsikoteers,

i am planning to have my alternator changed this saturday with a higher amp rating. i noticed lately na nag-didim yung lights ko whenever i turn on the stereo at night and mahina charging niya sa battery ko (the guys at the motolite shop i visited confirmed this). san kaya merong ok na shop na nagbebenta at nag-iinstall ng surplus na alternator? me mairerecommend ba kayo mga pare?

thanks.