I bought a heated hose with my 420E before days of the the piggyback cable.
I recently asked SleepZone about the possibility of an upgrade cable, and whether it would overload the 420 power supply.
SleepZone assured me that using the piggyback cable would not overload the 420E power supply. They don't make un upgrade cable so I got my local TV repairman to make a Y cable with the right size plugs and socket for me. So now I can use the heated hose transformer while I'm at home an turn the hose off separately, but take the Y cable when travelling and save space and weight by leaving the transformer and 4-point switched power board at home.
I think however that there may be several different 420E power supplies depending on where you buy it. Mine came from Tyco Australia and is Powertech MP3240 100-240V input, 12V 4A output. As the machine itself only uses 0.75A at 20cmH2O and the heated hose uses 1 amp, there's power to spare.
The 420E manual I got says the power supply module is a Class II power supply with output 13V 1.85A, but it has a sticker pasted under that saying:
"CAUTION - TYCO AUSTRALIA authorises the use of one of the following power supplies:
. Powertec MP3240 ... as above ... this power supply is standard for use in all regions;
. Egston N2GFMW rated at 13V 2A for use in Europe only (optional)"
The sticker is pasted over the words in the original manual:
"Power supply provided with the device Egston N2UFMW 24W 13V or ANAM TA2412 24W 12V."
24W at 13V would be 1.85 amps and 24W at 12V would be 2 amps so the total of 1.75 amps for the hose plus the machine at full speed would still be within the rated output of these power supplies, but not by a great margin.
You might ask the guys at SleepZone to reassure you that using the piggy back cable with the power supplies issued in the USA or other countries is really OK.