Still have only a 100VA transformer which was purchased way back when I got my first 100V player. It runs an LD player, two Muse decoders and surround processor fine. If I try to run a second player only then does it get a little warm; so I don't do that.
So you should be fine with 300W for your needs (for the purposes of rating a transformer VA/W are basically the same - I think VA is more correct; it's a technical thing to do with resistive vs non-resistive loads). I do plan to upgrade, so in my case will jump right up to 1000VA so then on that overkill I can then run multiple players without issue or worry! Easiest way to check is to add the power ratings of the equipment you're using and allow a little headroom too.
Also what I'm using is a fairly good quality one; a toroidal isolation transformer from Tortech here in Australia. I think a lot of the cheaper ones might be autotransformers?
https://www.gstransformers.com/technical/difference-between-isolation-transformers-and-autotransformers.html Personally after spending the money on equipment I'd rather invest the bit extra in the transformer for a cleaner/safer supply and peace of mind.