I raise triops quite a bit (not for food). I had good luck with just any old sinking fish food pellet that I can get from a petstore. When the triops are small I just crush the pellet very fine.
Also what size newt are you feeding the triops to? Triops can get up to two inches in length and are know to be able to eat amphibians. Also triops thrive in warm water so I'm not sure how well they would survive in cold temperatures that caudates live in for long periods of time.
I'm not sure how much nutrients they'd offer to caudates either. If you get it to work I'd be interested to hear how it turns out.
Also, why triops? There are plenty of other perfect foods for newts. By all means give it a go, but is there any special reason why you want to feed them triops?