So I have my adsl router on a dedicated ups for when the power trips or goes down, but sometimes at changeover from mains to battery, the adsl modem freezes and locks up. I can't ping it or log in and only a hard reboot sorts it out. Now my question is - can one run ups's in series? Can i plug my router's ups into another ups giving it double protection? Surely the output from the first ups is normal 220volt and powers the second, router ups just like mains does? Or will the second ups not like the source power coming from the first ups? Thoughts? I don't want to blow anything up or start a fire 