It all depends what you mean by worse. I think there is no safety or health issue (and the right place for evidence is in this question: Are WiFi waves harmful?). But if the question is wide enough to include RF interference, then the answer is yes.
Interference is caused because domestic power lines do broadcast the high frequency signals used to transmit data. In some circumstances these cause much more interference than Wifi (which is more tightly regulated and sits in reserved frequency bands where it won't interfere). This is something that is likely to vary from country to country but the UK story is told in this Register article (also a good source of primary links to the regulator and the key evidence.) The key section reports :
PLT [power line telecommunications] involves sending radio signals over mains electrical wiring for home networking, but given the lack of shielding on electrical wiring those signals tend to leak out and can interfere with anyone else trying to use the same frequency. Currently that only hits radio amateurs and those listening to shortwave radio, but faster PLT kit goes higher up the dial and has attracted concern from the Civil Aviation Authority as well as taking out DAB broadcasts and MW transmissions too...
The UK regulator, OFCOM, has, so far, not been persuaded to act despite some power line kit clearly breaching the interference regulations.