right. As mentioned, the RS-20 is too small.
Most 100 watt DSP-based featured transceivers (the FTDX101, FTDX10, TS-890, IC-7610) need about 23 Amps in transmit mode at 100W out. A 20 Amp supply will be overcurrent at that level, and might even start its foldback current limit which would cut the output voltage to protect the supply. And then the radio would shut down.
It would be best to get a supply that will be rated for the 23 Amp load continuously, which is at least a 30 Amp intermittent rating. If you want to upgrade your Astron linear supply, may I recommend the RS-35M. I have 2 of these and they work flawlessly.
73, Ed