Hi, welcome to Spider ID. 🙂 This looks like it could be a male False Black Widow (Steatoda), I’m not certain of the exact species.
I think you’re right. The way the triangles on the abdomen are deteriorated a bit in the middle gave me pause because that makes it start to look like other things. I saw a lot of Steatoda listed for Australia that I’m not familiar with but being Tasmania that narrows down the options. 🙂
Its one of the spiders New Zealand and Australia share