Guess you'd need to know the current draw of your UPC1237, thats 3W 12V.
I made the
K4700 kit in the end - only needed one - £17 inc. VAT. Les W. detailed the 0V separation to use one unit on both channels in an earlier thread. (I can find it again if necessary). Mine's been working for a couple of weeks now. Just another option, maybe not preferrable to you as you have the UPC1237 already.
I use an Avondale SSM2 soft start to feed the 820VA tranformer and 23000uf x2 per channel. Even with it, I still managed to blow a 5A fuse in the test plug when switching it on second time around, so now I'm on a 13A fuse. It should in theory also protect switch contacts by restricting initial contact load... so I didn't bother with that idea either lol... see my earlier picture of the short from the input switch across the thermal cut off contacts.
As for whether you need it or not... if you are not worried about initial high load through the inlet circuitry, a growl from your transformer as the core fills up, and it doesnt trip your RCD/RCBO etc. ... then no worries. I however, being new at this, am wary by what I've read and have put it in regardless. Slow blow fuses come into this equation also. 300VA apparently you are ok, 500VA you may be able to get away with just a slow blow fuse of the right rating??
Maybe, someone with fab experience can cut in here and put us all right?