What's the difference between a Legacy PowerMaster and a Legacy 360W PowerMaster?

As mentioned, these allow you to run conventional engines with the Cab2.  If you run only TMCC or Legacy, you do not technically need these (the DCS TIU has the capability built into the variably channels). Some folks use it as a way to connect power from the PowerHouse to the track without cutting off the PowerHouse's molex plug.  Basically, using it as a very expensive TMCC Direct Lockon.

The PowerHouse's molex plug, on both 180 and the 135, fit both PowerMasters.  The PowerMaster has one plug for one PowerHouse for a maximum of 180 watts to the track, while the PowerHouse360 has two plugs so two Powerhouses can be plugged into it to safely combine their outputs for 360 watts to the track.

If you are not using a PH135 or PH180 with the molex plug, but a different transformer, both the PowerHouse and PowerHouse360 need the same adapter plug for the molex connection.  They look like these I got off a forum post from gunrunnerjohn.  I use all PH180s.

(Deleted picture)

Both PowerMasters adjust the voltage from the transformer and produce a chopped sine wave.  I don't remember, but I think it is best to use a transformer producing a smooth sine wave so you don't get a chopped sine wave being chopped again. 

 ADDED:  See post below - I added the wrong picture so I deleted it.

The cables shown in the picture in the previous post are TPC3000 Power Cables from I.C. Controls.  The dual connector cable in the middle allowed two 135 watt Powerhouse bricks with their formed plug to be connected to a TPC3000 Track Power Controller without modifying the brick.  The single connector cables are used whenever one or more standard transformers (or two ZW outputs) were connected to the TPC3000.  The TPC3000 supported a maximum of 300 watts of input power.

IMO, there's very few instances where you need more than 180 watts of power on a single power district, especially if you're running conventional mode.  By it's nature, you'd be running one consist in conventional mode from a single variable power source.

That being said, I think the Legacy PowerMaster 180 is all most people will need.  Stick the PowerHouse 180 brick in front of it and you have 180 watts of variable power for that power district.

The Legacy PowerMasters are a nice step up from the old TMCC PowerMaster, they offer 200 speed steps as well as macro commands for MTH PS/1 and PS2/3 engines to access features not normally readily available on those engines.

GregM - Isn't TPC 300 and 400? (which subsequently became TMCC 300 and 400 after Lionel bought the rights to these products)?

If I remember correctly, the IC TPC3000 and 4000 did not have compatibility with MTH's PS.  When it was upgraded to allow keystrokes to operate PS functions, it became TPC300 and TPC400.  When Lionel bought the system, it kept the TPC branding (TPC 300 and TPC 400).  It was never TMCC 300 or TMCC 400.  As always, I could be wrong.

I don’t remember a TPC4000,  I still have two TPC3000 units and a set of cables.  My recollection is that when Lionel bought up IC Controls that was when the TPC300 and TPC400 units came into existence.  Don’t remember when the units started supporting PS1 commands.  The TPC400 was specifically marketed as a way to supply up to 400 watts to a single track.  Also, if memory serves, Lionel was pushing the new 180 watt Powerhouse bricks and the TPC400 was touted as allowing all of the wattage available from two 180 watt bricks to be passed through to the track, whereas the TPC300 maxed out at 300 watts even if two 180 watt bricks were attached.  I’m old too, my memory may be off somewhat.

CAPPilot - Perhaps my confusion stems from the fact that in a previous Post (dated 16/10/16) entitled "FS: Lionel Track Power Controller TPC 300 plus command base cable" the OP includes a photo of what appears to be a Lionel Owner's Manual entitled "TMCC Track Power Controller 300/400 (TPC)".  Check it out for yourself.

You really don’t need a 360W Powermaster unless you have a train drawing so much power that it trips the 180W version. I have a Canadian Pacific set with an ABBA full of numerous Pullmor motors pulling 10 aluminum cars with incandescent bulbs. Switching to the 360W version solved my problems. 

Regarding Lionel’s requirement for pure sine-wave input, I have found that you can get away with a chopped wave input at 18V if you add a hefty bi-polar capacitor across the input terminals. Otherwise, the chopped wave input will cause the Powermaster to produce some undesired DC offsets, tripping horns or bells.  

GregR - I can relate to what you're saying about the 'power draw' of your CP set.  Incidentally, you must be talking about Lionel item #6-21759 that was released on or about 1999 or 2000, which I also own.  Like you, I collected ALL of the cars (including the Station Sounds car) and as you described it takes a lot of power to run the full consist with the ABBA engines (two of which are dual-motored).  In my case I eventually decided to connect 2-180W Power Houses to a TMCC 400 (TPC), because before that, I sensed the 'current draw' was dimming my home's lights (lol).

Since we seem to be getting off track a bit, I use PowerHouse360s on my main line with TIUs in passive mode.  As gunrunnerjohn has pointed out many times, 20 amps (360 watts) to the track makes a good welder.  To prevent excessive sparking (and welding) I use the PSX-AC circuit protection board, an incredibly fast electronic circuit breaker with an internal TVS (plus several other functions).  The PSX-AC can be set to activate at different amperage levels, and I have mine set at 15.8 amps.  Below is my power setup with the PSX-AC.  The PSX-AC does degrade the TIU signal a bit, so the choke is needed.  If you are Legacy only, there is no need for the choke.  TVSs are cheap, so I use lots of  them for reasons discussed in other topics.

Note: The diagram shows the two PH180s being connected prior to the PM360.  The PM360 actually has two plugs, one for each PH180.