UPS Square wave AC - OK for A/B PLC power?

I have some A/B ML1500's and SLC5/05's that need backup power. I bought a UPS but a sticker on it says its output is essentially a square wave. I searched the forums and some people said that PLC inputs require true sine wave (probably due to harmonics).

In my case my inputs are DC, I just need AC to power the PLC in the event of power failure. Will this damage the PLC's or cause other issues?

Thanks!