I think this is something where shipments specifically headed to Russia were targeted. But that's not to say it can't pop up elsewhere. [typo edit]
i remember a classic demo at one conference where they used a PSU. It had some advantages: 99% certain it will be used near a computer. USB and Ethernet ports for "power surge protection" that can add attack vectors.
the only reason i can think of for irons is either lack of other opportunities, or trying to be as inconspicuous as possible (tech savy people are more prone to opening a PSU than an iron)
Wifi from inside a grounded PSU casing inside a (possibly metal) PC casing doesn't sound like something that's going to work very well?
ah, sorry... i wrote PSU... my bad. not a PSU, but one of those UPS, or no-break. more specifically the APC ones that are cheap and have USB data port and Ethernet/modem filtering.