What spider has a black body with ayellow triangle on its back?

From your description it sounds like the Golden Garden Spider (http://www.sdnhm.org/fieldguide/inverts/argi-aur.html) or the Saint Andrew's Cross Spider (http://www.austmus.gov.au/factsheets/st_andrews_cross.htm).

Is it this one?

https://www.askmehelpdesk.com/entomology/another-what-kind-spider-119971.html#post563878

Or maybe this?
Cobweb Spider - Steatoda triangulosa (http://www.cirrusimage.com/spider_cobweb_Steatoda.htm)