power consumption too high

Hello,

I have 2 rigs, both working stable 27mhs:
1st is I ordered from net and have consumption 900w from wall.

6x Gigabyte RX 470 GPU OC
Celeron G1840 Processor
Biostar TB85
DDR3 8GB Memory
Team 120GB SSD Harddisk
EVGA 1000w power supply
windows10

2nd I built myself and have so far 1300w from wall after -70 undervolting in MSI afterburner, 1100core/1950memory:
5x Strix RX 470 GPU OC - I will add 6th when power consumption will be much lower
Celeron G1840 Processor
Asrock H81 Pro BTC rev.2
DDR3 8GB Memory HyperX
Kingston 120GB SSD Harddisk
EVGA 1000w power supply
windows10

question 1: how it's possible that 100w PSU draw 1300wats from wall, (it was already 1400 when not udervolted) 250w when booted to windows 10
question 2: how can I drastically reduce power consumption, when similar rigs draws around 800 on youtube ???
question 3: can I also modify something in motherboard bios, CPU, RAM to reduce consumption?

Thank you!