Rather surprisingly, the PO Modular system has an unusual power connector compared with say, typical desktop synths or effects pedals, The dimensions are more commonly found with Japanese equipment and the polarity is reversed. TE don't ask too much for the PSU from their own store either, but add the VAT and shipping and it gets expensive.
Thomann's price is a little cheaper and while the minimum order amount is more, to avoid paying shipping you can usually find more things you need. Unlike the many third-party PSUs you'll find (even though this is really an OEM one as well, not TE designed or styled, and unbranded) this is not a wall-wart and it has a detachable mains cable so it doesn't matter if it's two-pin, three-pin or whatever that you order. Mine's running off an IEC power distribution board. No hum, no noise, and can even be attached to the POM-400 body.