There are (at least) two different types of slas.
GellCells, and regular lead acid batteries that
are sealed.
I have only used the GellCell variety.
It is hard to get a AC mains powered supply really quite.
You can reduce maybe 99% of the noise.
Most of the time that is enough. Givent he local and worldwide
noise 99% is below the noise floor most of us deal with.
For me the biggest advantage to using a gellcell is for
emergencies. When the lights go out I an keep listening.
I have a Lamda 12V rated at 8Amp, but will deliver about 14A
before going into current limiting, power supply that I bought for
$10.00 from a local surplus dealer. Big ugly and heavy.
No meters and a barrior strip for the AC mains 120V and the
12V out. It was already wuite, but I added some more noise
suppression. A Coreman heavy duty double stage IEC female
power connector to help keep it's noise from getting back into the
AC mains. I bypassed all 8 of the bridge diodes with 0.001uF
mylar to help prevent IM via the diodes. I added several ferrite
cores to the +12V out. I drilled a lot of additonal holes to add
1 connector (more or less) to the case halves for better RFI
"containment". I added a 120V 60HZ relay to open the PS +DC
output and a connector for my gellcell, a 24A/Hr panasonic unit.
I replaced the single turn voltage adjust pot with a10 turn unit
that Imounted onthe case. I keep it adjusted to +13.69V, the
suggested "float" volatage for gellcells.
It has worked great for several years now.
I power all of my 12V equipment from this single supply.
The main advantage being that it is much quiter then the
built in supplis on my radio and scanners, and I only
had to cleanup one supply instead of five.
Does it make a dffference, yes. My shack is much quiter,
that is has much less RF noise and I can connect any of the five
receivers/scanners to 120 and use the built in supply and
the noise floor jumps over 10dB.
I have also added the best ground I can afford. Used double shielded
coax for all my receiving antennas and connected all my equipment
with 1/2" tinned braid to a single grounding point.

Terry