Dual power supply (relay?)

Hello,

I am running a prusa I3, ramps 1.4 arduino package with a relay to power heated bed.

I cant seem to find any spot on discussion about this topic, hence this post.The printer has been working fine up to the point where I need to crank up to 110c for ABS

I have attached specs on power supply.

Relay attaches to D8, and the firmware is set to run in bang bang mode.

I have used cardboard as an insulator from the aluminum y plate below, and seems to work fine. I can hit around 100, but upon removing heated bed cover (cardboard) the temperature drops about 10c and never returns (full output). The bed is a large 8.4 x 12.6 PCB link below

[www.makerfarm.com]

I have a spare ATX PSU that I can use. How can I go about either:
1) Squeezing more power to heated bed
2) Hooking up two power supplies to ramps / relay?

Thanks